I think I remember bisjac said this in a previous thread, and i dunno if it was posted yet
basically, the mlp thing started when 4chan thought it would be funny to start liking/obsessing over something as ridiculous as mlp. However, people who genuinely liked the show thought that people were being serious so they came out and spread it around. Now it's gotten out of hand because theyre trying to fit in with the "cool kids"
basically, mlp is a joke taken seriously by some strange people