- They're pregnant. A lot of guys don't really feel like dealing with a woman's pregnancy, especially when they just got to know her/barely even know her. A lot of responsibility. Puts a lot of pressure on them. - They're about to have kids. A lot of younger guys aren't ready to deal with kids, especially when the kid isn't even their own. Again, a lot of responsibility.
Dating is supposed to be fun, relaxing, not about commitment straight away. If/when you bring pregnancy and babies into the picture, it immediately puts a lot of pressure on the guy. Especially if he's not ready for that yet. And a lot of guys are not into the idea of raising another guy's kid, or being there for the kid for a while but then having to leave if/when the relationship doesn't work out. That's clearly not fair to the kid. So yeah. Lots of unwanted responsibilities and pressure.
Crazy enough, I am in this situation right this moment. I met a woman at my job that works for a diff company, that I get to interact with a few nights a week with. We have been hitting it off, but I never thought to take it any further cause she is preggo. I found out that she is interested in me and the baby's father wanted nothing to do with her after he found out she was pregnant. It is abit too much for me to handle though, I think. That is skipping a lot of steps to get involved with her now.