Those are skills that I can explore without paying, though, without 'experimenting' on a client. With people that I'm attracted to and therefore more likely to engage with, at that. Or in the specific case of kinks there are some very good classes and workshops I could attend, rather than hiring another escort who may or may not be proficient.
(As it happens I've been into BDSM for most of the time I have been sexually active, and so am pretty proficient in bondage and other associated activities. I've done a few duos with other kinky escorts selected by clients, and been horrified by their lack of skill, and some of the risks they took with the client, which I would not allow them to take with me).