Why does it appear to be the case that if someone has a child, that's a turn-off for potential romantic (or "romantic") prospects?

I don't think I have any recent empirical evidence to support this - my romantic (or "romantic") life recently (the last few months, call it) has been abysmal at the very best*, so I don't really have an actual basis for my suspicion. But that's what I've noticed, in general.

* With responses ranging from "um. *conspicuously absent*" to "ha, no. Wait, you were serious?".