Why not? A lot of things from the 80s and 90s are making a comeback right now. I had both Transformers and My Little Pony toys (I'm a girl born in 198cool and one has a series of movies produced by Spielburg and the latter is reborn by a fan of the first generation.
In my opinion, it's lighthearted, cutely designed, yet at the same time, not sickeningly girly.
I hate the growing trend of media where the main character(s) are too stupid to live. I used to hate Johnny Bravo, Ed Edd n Eddy, and Courage the Cowardly Dog and even the Twilight series for this reason. Yes, there are times characters in MLP do things that make me introduce my head to the nearest hard surface, but they learn their lesson in the end.
And to be honest, I don't see the appeal of Adventure Time, while my boyfriend's cousin loves it and Ben 10, but whatever floats your boat.