If they can't come up with enough to talk about online, then they sure aren't going to have much to talk about in person, IMO. They just get bored with the talking part and want to move on to the physical part.

There's this one guy who comes up as a perfect match for me every time. I've contacted him. He's replied. We're both interested in getting to know each other, but he's got a hectic weekday life and doesn't reply very often. It might take him 3 or 4 days to get back to me. Drives me bonkers. But he's got all of the things I'm looking for and looks to boot, so I'm being uncharacteristically patient.