Well, I've watched MLP since the very first episode in 2010, and let me tell you, it was a cartoon that I and a lot of people had been waiting for a long time. Before 2010, the majority of 2000's cartoons were mediocre or had no care to them.
MLP FIM was something different, it had care and thought put into it. That's one of the major reasons why it became popular.
Those other cartoons like Teen Titans Go, are nothing more than "Hey Kids like weird and bizarre stuff, lets just make it wacky without any thought put into it, and lets cancel the awesome "Green Lantern the animated series" while we're at it.