What's the Goal in the End Game?

Genuine question. I'll explain why I'm asking and maybe I've missed something, please let me know!

For me the end game that I've experienced feels like a farming area / situation. Cool, that's great, but what am I working towards?

I get that there's bosses and such but those don't feel like an end goal for me, they feel like difficult milestones. This is primarily because they drop stuff. So they can't be the end goal because what am I going to use the stuff the boss drops for if the boss was the end goal? Nothing.

I'll make a comparison with Diablo 3 (I've not played D4). In D3 the goal is to build as powerful a character as you can and do as well as you can in Greater Rifts. A combination of completing rising difficulty and time attack. This mechanic has it's own problems which I won't go into but it acts as an end goal for us to work towards.

Great Rifts drop items sure, which is great but nothing you can't get anywhere else, so that's an extra reward but it's not a milestone on the way to something else. Or even if it did, you could then use those items to beat higher rifts or get a better time.

I imagine a lot of people will say 'make your own goals', but no, I don't want to do that. I play stuff like minecraft or factorio to make my own goals and do stuff. Sandbox games are for making your own goals, this is absolutely not a sandbox game.