From a different perspective (not taking D/s or other kink into account), in my ample dating experience, I've found that women who want a "friends first" or "take it slow" approach almost unfailingly end up not interested in dating me, and often times are dating other guy(s) in which they developed a stronger chemistry within the first 3 dates. Many men want to avoid unclearly defined relationships in which they are pursuing her for dating purposes and she is allowing him to treat her out, go to events as a couple etc, but she doesn't have the intention of dating him. Men feel taken advantage of in situations like that. Guys would describe a woman doing this as "leading me on".
So, some of the more dom type guys take the opposite approach -- they apply the "3 date rule" and screen out women who aren't interested in expressing their chemistry physically. The idea is, if you're not feeling it now, you most likely will never feel it. Plus, if he's investing that amount of resources in pursuing somebody who's holding out, the risk (opportunity cost) to him increases dramatically (he could have been pursuing someone else more interested in him).
Please note -- I'm not condoning or criticising either approach, just that I understand why men would behave this way. When I'm in my more extroverted/Dom moods, I have applied the "3 date rule" to great success. Of course, that filter leads to finding sub girls. It would certainly not work if i was seeking a Domme.
Some guys are trolling for sex and nothing but -- they want an NSA casual encounter pure and simple. They are misguided. The Net is NOT the way to acheive that.