Once my original save got to the endgame, I spent a lot of time maxing out my money, freighter, bases, etc. and contributing to the glyph exchange subreddits. After a while I stopped playing but would check back in after a major update. I didn't really play again seriously until the expeditions started. It's the game I often go back to when I don't have something else to play.
A lot of people find that civilized space is the thing that gets them to stay engaged in the end game. Helping to contribute to a community, helping new players, opening your own business to provide resources, stuff like that. I, of course, recommend the Galactic Hub as your first consideration for a civilization.
They said there are 4 Quadrillion stars and each has at least 1 planet you can land on. While true, each planet is one of ~8 variations and that's it. Like... snooooze. Then they just added shit like underwater bases which were useless.. or new underwater vehicles which were useless.
That's like saying a sandbox is only sand. It is what you make of it. It doesn't need to be deep if your imagination is. Granted, that won't be the type of game everyone enjoys. But for those who do enjoy it, they end up putting in 2,000 hours like me, and I've seen plenty of people with more hours than me too.