it's probably because ponies have some human-like traits that can be considered attractive, i guess. big eyes, long hair...which is usually what makes a human female attractive to people.
it's been going okay so far, even though there were some bad episodes during its run. i haven't watched all of the episodes so that's pretty much all i have to say on this matter.
it's probably got to be the discord episode. a few minutes into it i got kind of bored so i just turned it off. i guess it didn't appeal to me very much.
bronies/pegasisters making a ridiculously big deal over the fact that they like ponies. i mean, in my opinion, it's nothing really that special, other than that you're outside the target demographic.