We haven't had an analysis post in a while have we? I guess the lack of episodes does that. We've also only ever touched on this subject once or twice (primarily as an April fools joke). As with most things on the internet, the usual Rule 34 didn't skip out on ponies. But why is it a thing?
Obviously there are a million possible answers to that question, but this one tries to explain it from a biological level. If I were to give this a rating, I'd say it falls somewhere around PG-13, so feel free to pass over it if you are squeamish.
For everyone else, get an analysis with the usual fast moving images below!