Ben Wyatt came to Pawnee as a state auditor because Pawnee was bankrupt. He came with Chris as a team, they were friends from the start. After a couple weeks in Pawnee he started to like it more and more. eventually he loved it and didn't want to move away.
One of the reasons Ben started to like Pawnee was he loved Leslie. They got married really suddenly. And just recently we found out that Leslie is pregnant with triplets.