Board Thread:Questions and Answers/@comment-27279772-20160710120721/@comment-5956954-20160710135218

Since he is one of the most hated characters canonically with the monsters in the underground, Jerry has his own house in Snowdin Forest because he was exiled from the main town (Snowdin Town). Jerry is also encountered only in Snowdin Forest as a battle monster and not as an overworld NPC like the others like Snowdrake and Ice Cap.

That is my theory.