Totally unscientific, 100% baseless opinion here...
Perhaps the concept is that a guy that is on PreP / U==U / etc, is doing so many frequent tests that they likely don't have anything to transmit.
Meanwhile, a guy that requires condoms may never have been tested for anything (figuring the condoms are all the protection they need) and thus may be carrying something transmissable? Oral, kissing, fingering, even just their jizz getting on you, all could be risky depending what they might have?
So yes, condoms give safety for the act of sex, vs going bare.
But for the overall encounter, might playing with someone who requires condoms be less safe than playing with someone prepared for bareback?