One of the reasons (as other posters have said) is the freedom that is often associated with it, particularly the UMC. I actually come from a mottled background. We were raised in a United Methodist Church - my mom has always been Methodist, my dad converted from Catholicism - but we weren't really raised that way. My dad would basically listen to any preacher back when I was a kid, and so my upbringing is probably a lot closer to a dispensational, fundamentalist Baptist one rather than Wesleyan, even though we called ourselves Methodists.
When I was in High School I had an increased interest in belief systems, and particularly the more esoteric parts of Christianity's and Judaism's histories. Out of necessity that meant that I started looking at Church History, which shed more light on the Catholic Church primarily (my dad had generally been negative about his past beliefs, and we grew up with all sorts of misconceptions). Gradually I took more of an interest in orthodox theology and made my way back to looking at Methodist belief.
By that time I was already decidedly mainline or moderate in my beliefs, and distrusting of many of the things lingering around from my childhood. When I looked at what Methodists actually do believe, I was very surprised to find that I agreed with most of it, far more than superficially too, in which it put me at odds with how we'd been raised. I've mostly gotten over that conflict now, but it was very reassuring to find out that the church I'd known since childhood really was where I fit, even if it wasn't the vision of faith that we'd been raised to see. I'm more or less ambivalent toward 'High Church' practices, and actually prefer those somewhat, and generally dislike the 'Contemporary' side of things which is so popular now.
Despite that, considering how I came full circle here, I've made my faith fairly open-ended. I admit things which those in situations like my childhood produced would have a religious crisis over, but I've realigned my priorities and nothing like that can really phase me anymore. Faith is far more personal to me now than it ever was, to be honest. It's just not a make-it-or-break-it deal anymore - it's fluid, now.