Add-ons

It's because of bad interface design and too many bookmarks: First, browsers add bookmarks in some menu instead of the toolbar per default. Then the toolbar in many browsers starts cluttered with useless presets. Then, if you have the bookmark added to the toolbar, it overflows into a toolbar menu, hiding the newest most important in it. Then, once this fills one screen, the new bookmarks are still added at the bottom, but the menu becomes scrollable. So to reach your bookmark, you have to open menus and painfully scroll in them without a scroll bar. Often, depending on browser, scrollwheel doesn't work well inside.

Now you can try and organize most bookmarks, like keep the tabs in their own quick access folder. But now it's hidden again and you have to remember to clean that up, which you forget, so it grows and you're back at the scrollable menu problem at some point.

All this teaches users it's faster to pin tabs or use session restore and leave tabs they will need later open, using bookmarks only as a last resort or backup they usually never need.

One simple help is adding bookmarks at the front and having toolbar as default folder, but that requires extensions, if it's possible at all depending on browser.

I use bookmarks for stuff I may want to access later (as in another day), not stuff I want to access within a few hours. If I used bookmarks for everything my bookmarks would be even more inflated and unorganized than they currently are. I'm not one of those people who keeps hundreds of tabs open for weeks on end, I just have a habit of opening tens of them each day. I usually close my tabs once or twice a day anyway.

Also if you have a low amount of RAM (which there are some that still do), you may not want to only have 2 tabs open at once. Sometimes it's much more convenient to just leave stuff open.

You do have a bit of a point though. I could start using bookmarks instead of pinned tabs for some things, and I guess a good bit of it boils down to me being unorganized.

Perhaps, but this allows you to do it instantly at will. Like if you only have 8GB of RAM or something (or even worse like 4GB), and RAM is getting tight, you can just right click on your current tab, and press "Unload other tabs", it unloads all but the current tab (except for pinned tabs, you usually need to unload those individually). Like I said not super necessary if you have high RAM like I do now (32GB), but just 2 years ago I still had 8GB, and just 5 years ago I had 4GB (single channel in both cases). This extension actually doesn't automatically do it AFAIK. It's only manual.