Usually if someone is so unatractive they are desperate to get laid so the intimate encounters work great for them...usually neither party is concerned with looks or personality....and also...anyone who probably doesnt charge for having sex anymore...due to age...or...STD issues....
That isn't really the case. What I've noticed primarily is that the adult dating sites/intimate encounters are used by those searching for a more stringent set of specifics. Discrete or No-Strings, exploring specific fetishes, interracial, group/swinging, age differences, bi-curiosity. Things they can't approach in real life encounters and things apart from traditional dating.