GermanParamedic said:

Anyone would please explain me why MLP is so popular?

It is so popular in grown men and teenagers and children alike, because it is the type of thing that just one episode it is almost relatable, the characters are quite cute, sometimes it is humorous, and almost everything is very lighthearted and "fun". The rule 34 of it is probably due to the characters being so lovable and/or cute (like this version of Rainbow dash) or hot in a way (like button's mom). Why I like it is the fact that they are the type of character that you just wish you could hug like, especially Fluttershy.