Pinkie Pie has a secret Dungeon, Invitees only. A while back, she had the idea to go out into the world outside to see others. Going from the Dungeon felt natural to her. In this case, she wanted a new mate to play with.
I just recently started to write stories directly towards the FiM actively, though I have been writing for years, publishing numerous stories at Mibba and the eventual pony story, as far as to the MLP