I don't think it's very fair to pigeonhole every guy under the same umbrella excuse. I think there are a lot of factors.
Some of us just might be insecure and fear commitment, fear letting someone down, fear screwing up.
I'm of the opinion that if we're talking about normal, sane men.. not assholes who would cheat or dodge a relationship no matter the circumstances. It's really not as maniacal or evil as some people want to let on.
I think it boils down to a guy's personal insecurity. By winning over another woman or seeking out another woman, we feel liberated. When we answer to one woman, it's not easy to keep all of our needs satisfied and I don't just mean sexually. Guys are selfish and you really have to go out of your way to make sure he's happy. I don't think that's fair but I think that's part of the problem for some guys.
I will admit that years ago, I led one particular woman on for a couple months. And for myself, I just didn't click with her. We were friends and I didn't stop her from becoming attached to me. It's hard to tell someone how you really feel sometimes, especially if you know they're more interested and it will hurt them. But again, this is under the assumption the man respects you.
If you ask me though, if you meet a guy who can't communicate even a little and there's an average amount of chemistry, you should just move on and just stay friends if he's mature enough to have a female friend he doesn't have to sleep with you to stay in touch with.
because they want to keep that option open...my experience has been that the 40+ men are the ones who want to play the most...20+ men are the ones who want a relationship...and 30+ men seem to want it all...go figure :)