While working on the first Octodad, I was a bit overwhelmed trying to get the game done and keep up with my school work. MLP was a bit of a break to the insanity of constant work. Since all I had in my brain was pony and Octodad, it was only a matter of time before I drew them together.
But, you are right, pony has been crossed with just about everything under the sun now, even when they probably don't need to be. It is interesting how this fandom has decided to do this and I can't think of another fandom that has done the same. I wonder why that is.