I think late game in singleplayer can become boring fast once you have a safe base, but this will change in the future when NPCs are added.
Im currently waiting for multiplayer to be reintroduced, Im hyped since a year to play with friends again and online, too.
But I can only speak for myself, there are many other players which already survive over a year in SP and still have fun.
In my best game I had a nice cozy place, it was really safe, thing is Im not interested in building a really big base yet, this doesnt make sense to me when I play alone.
Also I really get carefree at this point and die.
But, this is just my opinion on the standard apocalypse mode.
The last thing I did was the winter challenge, that was a really hard, you dont even would think about endgame if you need food.^^
You are happy If you find a peaceful place to rest.