Reposting a comment I wrote in another thread that explains it:
Bookmarks are for things I’ll need to reference again and again in the coming years. I do keep a tightly-curated bookmark collection, I just don’t want it clogged up with a bunch of stuff I can’t foresee needing in the long term.
Tabs are for things I’m working on right now and don’t need bookmarking for the long term. And, for what it’s worth, most of the browser windows are custom-titled, so the windows themselves are a lot like bookmark folders, while the tabs are like temporary bookmarks.
Plus, the ability to search through tabs by hitting Ctrl+Shift+A means that it ends up being faster to search through my tabs than my bookmarks, without using the mouse. ex: Ctrl+Shift+A, Type needed page, up/down arrows if needed, then hit enter to move to the tab. With Ctrl+Shift+O, you don’t get the same ease of scrolling the results without tabbing through a bunch of junk first.
There are other reasons, including neurological ones surely, but those are my primary justifications.
Reposting a comment I wrote in another thread that explains it: