I'm a bbbj guy. I know exactly what the OP is talking about. FS is what I do with my FWB, exes, SB's, and once in a blue moon with my SO.
Only a few providers have brought me into the FS part. Not really my thing if it's not with what I've listed above.
Don't get me wrong though, I've enjoyed FS with all the providers I've participated in with but not the same for me.
For me, if I'm paying why should I do any work?? Guess I'm selfish.