JustWondering

It appears this is changing soon. WhatsApp is introducing usernames, and will provide the option of keeping phone numbers private.

It appears this is changing soon. WhatsApp is introducing usernames, and will provide the option of keeping phone numbers private.

It appears this is changing soon. WhatsApp is introducing usernames, and will provide the option of keeping phone numbers private.

Completely agree and i think about "why aren't providers/clients all on Signal or Threema?" a lot too. I have the same critiques of WhatsApp and all Meta/Facebook companies in general. I greatly dislike using their products/services and options like Signal or Threema are better in terms of privacy/anonymity.
WhatsApp is widely popular mainly just because it'd already been the most widely used messaging app globally for a long time. It was one of the first messaging apps that really took off in widespread use during the times when regular SMS/MMS texting used to cost money, especially for international messaging. It's never lost that first mover/most popular app advantage.
You may be aware of a lot of this, but under the hood, WhatsApp actually uses the same open source encryption protocol that Signal created and uses. The WhatsApp messages contents are truly encrypted, by default, in transit from device A to device B to the same level as they are on Signal and Meta can't read the messages. Which is actually a notable advantage over Telegram which does not encrypt messages unless you activate "Secret Chats". Which you have to do separately with each individual person you're messaging. Telegram's encryption for Secret Chat's uses MT Proto 2.0 protocol which is Telegram's custom, but mostly open source, encryption protocol and to my knowledge it works similarly but it's not the Signal protocol like Signal and WhatsApp use. Check this out for a deeper dive on WhatsApp encryption/data handling: https://www.securityhero.io/is-whatsapp-safe/
The same is true for Google RCS texting. RCS is the replacement to SMS/MMS that Google uses a closed version of (there's an open standard version but Google and phone carriers made it so that version doesn't get updates to make it usable for third party texting apps like Textra or other texting apps) and is the default messaging app on nearly all Android phones. It also has cross compatibility including encryption with Apple iMessage as of fairly recently, so iMessage texts with an Android user no longer fall back to SMS/MMS but to RCS on supported iOS and Android versions. This is also another main way sex workers/clients communicate. It also is encrypted, but Google and the phone carriers have the other identifying metadata just like WhatsApp and Telegram do.
These big companies largely don't want or need the actual content of our messages anymore, but they do keep the metadata logs of who we message, when, where you are, device IP addresses, how much/long you use the app for, and other metadata (for years) and this is largely the info they are using to still build advertising profiles on us and to turn over to law enforcement when compelled to do so. That can then be what's used to get a warrant for a device search and they get message content from the actual devices of the users if it is still on the device.
The advantage Signal has is that the messages/underlying protocol are fully encrypted and open source, the user facing app and server code itself is also open source meaning you or a trusted auditor can actually check that the app functions the way the developers say it does (not the case with Telegram and Whatsapp), and 3rd party code audits repeatedly show that basically the only data they ever have is when you made your account and the most recent time you last used the app/pinged a server. They don't even have the metadata for who is messaging who and when, let alone message content. It's all encrypted along with the message content.
I feel like Signal isn't well advertised outside of tech minded/privacy minded people and spaces. It's most popular with politicians/government workers, reporters, political activists, and privacy seeking regular users. So i don't think many in the sex work space even know it's an option or they don't fully see the upside when WhatsApp/Telegram have the option to encrypt message content too (which of course is not the only aspect of messaging privacy that matters).
Signal also has the problem any app competing with an entrenched dominating competitor in it's field has. Getting large swathes of people, even those just among a niche group, to switch apps/services is always a near impossible task unless something monumental happens that causes a mass user exodus from the popular app to an agreed upon alternative.
 
This is objectively not true. Privacy is still a thing, and it's why the powers that be are still trying to increase their encroachment on it. Many countries/governments are still actively trying (and have not yet succeeded) to ban or gain backdoor access to things like encrypted apps or VPNs specifically because they do provide privacy.
Privacy is important, is still attainable to varying degrees if you're willing to become technologically savvy and give up/find alternatives to certain conveniences we're all used to in the digital age. Many just simply aren't willing to put in that effort/give up those conveniences or don't know how or don't care how to figure it out. Which is why those that feel the way you do default to that position. It's not that we can't, it's that you don't want/care to because the conveniences you get in exchange for your privacy are worth it to you. You don't understand or just aren't usually the one directly affected by the instances when that trade off is abused. 
And that's truly totally fine, but just be aware and honest about it at least. Lack of privacy is not at all something you have to just accept, and some semblance of privacy is something everyone needs to varying degrees. Whether you think you have something to hide or not (and whether you do or not is subjective and sometimes isn't always up to you).

WhatsApp seems to be the preferred messaging platform among providers, and I don't quite understand why. It's a Meta product. When it comes to privacy, they don't have a great track record. I've looked into it and my impression is that it's not really possible to use it anonymously. Maybe there are ways to protect your identity from the people you chat with, but the account itself is still traceable to your identity. I have a personal aversion to anything related to Meta, but it seems my concerns and my preference for chatting on RM is to my detriment, as it cuts out a number of people who only want to be contacted on WhatsApp. Is my worry unfounded? Why isn't Signal or Telegram more common?

In Rentboy you could block a provider and he would no longer appear in searches. This was helpful in narrowing future searches. (You could view the block list and unblock.)
I wish Rentmen did this. 

I hate that one of the filters you can search for is "travelers only" but not "locals only". When I have a place in mind I want to go visit and want to see what providers are there I don't want to be seeing ads of guys who won't be there when I will be.