it's so you can read their old books D:
got through the main quest of morrowind, have tribunal and blood moon to do now, along with a few faction quests and a house quest line to complete.
of the three games in the series that I played, I'd probably say skyrim is my favorite, then morrowind, and oblivion last. None are bad, it's just oblivion is too easy the whole way through. (That being said, I could always try OOO or something to make the game feel at least a bit more challenging)