The first time I hit max level I was confused as hell in DF. It's was not the lack of content. It was the opposite. I too tend to play alone most of the time. Maybe once a week my wife comes along.
I don't have a many contacts in the game. Most friends stopped playing. So I ended up alone. But there is a lot of content even then. But the game is not pointing you to it. It's not like "Oh you hit level 70, now you go and do this and that". It's there, but you have to find it yourself. You have to figure it out yourself. The first time I went to Iskaara for the cooking event I was overwhelmed. I didn't know what went on here. But I figured it out by participating again and again.
There is a lot content there, but if you wait for the content to be paraded in front of you, then there is none.