Props for being one of the few people to realize it's a tooling problem. The "umm why would you have so many tabs?" you always get on HN is a reminder of why most people are so bad at UX. Most people just can't see outside of their usage.
You're onto something here. I have a lot of tabs because it's a history of one thought to another. It's not just a set of tabs, it's a sequence of locations. Keeping them open is how I can remember to go back to them, how I can keep my state in them, and more.
I can envision a much better UX where your tabs become some sort of history entry where they are frozen in time (serialized to disk) and can be rehydrated. And you can easily scrub back to them even once they've been unloaded from memory and frozen. And you can create different sessions for different things, a window/session for today's HNing, one for today's work, one for play, etc. And you can reach back into historical sessions to load their state. And merge another day's session into today's because it had some outstanding tabs you wanted to get back to. And there'd be good ways to visualize this.
I know some things like tab groups and tab sessions exist. I personally use Firefox with tree tabs to get something like this. But there's more UX thought that could be put into it instead of just wondering why someone would want a bunch of tabs.
One of the main reasons I'm reluctant to close my browser and trash my tabs is because the exact sequence of tabs, what's open, the order they are in, the state on each one (like being paginated to page 58 in some in-browser book scan UI) is a snapshot of by brain and digital "desktop" at that moment. You're right, browsers do very little to help.