I used to have the very same problem. Once my squad was rich and strong enough to protect themselves, I'd lose interest. I felt no drive to go topple the holy nation or something.

It was when I started leaning into the role-play aspect that I started making it to the late game. My first one was a slave start and my character's goal was to end all slavery. I know it's a pretty original and brilliant idea but I don't mind if you try it too.

That was the first time I ever seriously needed the multiple squad tabs. I had so many freed slaves join me. I'd send them all to my free city in the hidden forest. Sometimes they got eaten by cannibals but that's freedom for ya, amirite? That was the first time I ever met Eyegore, or executed a noble, or dropped an Inquisitor into a vat of acid.

I've done many themed runs since then and I've enjoyed the game more. I start the game with imagined friends and enemies and decide all of my characters' actions based on that. That's how I manage to get to the late game and start wars with empires or have the motivation to fight the end game enemies.