For me, what keeps me playing even after 1000+ hours unmodded, is the exploration.

Each new seed world presents its own problem of logistics.
Where should I build?
What locations are near what resources?
What combinations of biomes that will make processing ore and transport easier?

Part of the exploration is finding key things. When you find stuff for the first time it is quite satisfying.
For example
Finding the Trader
Finding your first turnip seeds. <food is important to progression as much as metal for armor and weapons>
Finding your first source for entrails.
Finding silver without a wishbone.
Finding a good location for a plains farm.

A lot of people don't put much thought into the logistical aspects of it and just end up taking long trips by boat to haul stuff around... to me the game is all about trying to avoid that as much as possible. Not that I mind sailing around and hunting at sea, just the tedium of transporting ores back and forth. Some people cheat this through portals or world hopping but to me that avoids the best aspect the game has to offer.