It’s an honest question by the way. I don’t think I have ever felt the need to have more than 10 tabs open at the same time - that was when cross-referencing things in Jira - and I generally have no more than 5 open. I would like to understand what I am missing.
Speculating (extrapolating?) for someone who keeps a lot of tabs open: tabs represent desired history, closed tabs represent stuff they might specifically want to ignore.
It's almost useful to think of creating two "close tab" buttons -- one that sends the tab to the searchable service, and one that just ditches it.
Yes, it's basically an effortless replacement for bookmarks. Especially if you have Tree Style Tabs or equivalent, opening a link in a new tab creates a child tab that treats the parent as a folder. For example, the way I use it, all HN posts are children of the homepage, and the homepage can be opened/closed like a folder in the sidebar. These go arbitrarily deep, so interesting links from that thread become children of the thread, etc etc.
W.r.t. the difference to browser history though: I literally never find stuff when looking through my browser history. I either forgot on which website I found something, or what the name of the tab was. I sometimes wish that searching the browser history also searches through some additional metadata, like the sites description meta tag or something like that.