It’s about having fun. Maybe trolling. Not every person has the time or money to make the ultra-super-perfect costume, or has that “flawless” size 4 body, or the right contacts. Even a mediocre costume has a story behind it, and the person who made it does not deserve to be bashed merely for deciding to walk around in public while wearing it. This is even more hypocritical when some of the special-snowflake-perfectionist-lovers claim to hate fashion and refuse to “give in to the man” or whatever by not buying trendy clothing.
You’re doing the exact same thing you hate seeing in magazines and mainstream pop culture; judging a person by what they’re wearing or what their body size is. Give it up already.