we get bored and want something new. Sometimes it works out to be really great and sometimes not so much, for instance, my teenager wanted bangs so bad and I told her not to and she got them anyway...she's very petite and afterward she looked about 5 years old and I said "told you it was a bad idea" she couldn't grow them out fast enough, thankfully her hair grows fast and thank goodness for bobbie pins! but even with all that? she'll do it again in about 6 months because she'll want something different again lol ...girls what can I say? ;P
because they want to...why else would they get bangs?
I think that they look beautiful on some girls. The ones who pull it off well probably would not make you think they are unattractive.
On some girls they really do look awful though.
Overall I guess it is one of those girl trends that guys don't like but girls do, similar to a short bob, I find that most men don't like it at all but some girls like getting them and some pull them off really well even if it isn't male-approved sexy.