In all honesty it isn't really them that we are writing about, in most cases.
We basically take a pre-made character and make them our own, writing a story surrounding them.
I just think it's easier.
I write them how I want, whether bad or good and then write my own story.
It's also a better way to get feedback because it's more likely to be read. So, why not?
It's not like most of us are writing who we think they are. We aren't that stupid. We know we are making shit up as we go. That's the fun part.