While I can understand that point of view, Microsoft did studies and found that people learn static UI elements better than dynamic ones that shuffle around. How ironic then that they remade everything with dynamic ribbons, then re-remade everything with static ribbons, going back to their studies from the 90's. Sometimes you just have to change for the sake of change, I suppose...
I would use bookmarks extensively, but the UI elements to add, organize, and manage them have not kept up. We need something more akin to the Windows Explorer, to be honest - it's a great file manager that has stood the test of time since the 90's. Once I hit about 12000 bookmarks, I just stopped collecting more - it was taking way too long adding them with conventional UIs.
That's where tab usage comes in. Bear with me while I explain a use case, as this might take a few paragraphs... I'm also unsure how to word it in a way that avoids sounding arrogant. I'm in IT, but I handle support requests primarily from other IT people and businesses in my little corner of BC, Canada, and regularly handle a thousand or so support requests per week. (with no mistakes or missed details.) My colleagues have dubbed me a hyper-tasker due to the level of sustained speed and detail. But that'd be absolutely impossible without static UI elements. In this case features like tabs and Windows are basically UI elements for the tasks or data required.
I better get to elaborating...
Things that shuffle around slow people down, as now you need to search for the thing rather than go straight to it. Microsoft has published extensive good-UI-design whitepapers... and then proceeded to ignore their own research, a lot of the time. A good example is Alt+Tab - it rearranges previews based on what was last used, so if you have a few hundred things open, good luck ever finding what you want on the first attempt. I use 7 taskbar tweaker to fix that behaviour, plus taskbar behaviour. Alphabetical lists, thank you very much - with no previews. I decombine window stacks for that very reason.
Taskbars have tons of horizontal space - no need to jumble icons up and constantly rearrange them. I want the window for stock websites to be in one spot, the window for programming sites in another, the window for news sites in another spot, the window for /. in another, the window for printer remote servicing and on-site reset procedures in another, the window for videogame stuff in another, the window for looking up local business contact info in another, the window for web developer and Wordpress stuff in another, the window for electronic schematics for boat GPS systems in another, etc...
And when they get too many tabs, I just spill them over to another window, which goes beside the first. Since they are largely static, I can always find the right window for what I'm doing in under 200ms.
Then for tabs, I recognize the icons, and turned off all previews, then enabled keyboard shortcuts, so I can very quickly toggle between them. Again, each tab flip is under ~200ms (Depends on PC performance, but with Ryzen and 128GB, tab flips are always speedy), so I can do 5-10 tabs per second. Makes it quite quick locating what I want. Even if I mis-click and end up on tab 86 rather than tab 110 (out of 200 or whatever in the window), just hitting my keyboard shortcuts a few times gets me to the right spot. Since the tabs are basically a chronological history, I only need to remember roughly when I was working on something or looked up some information, and then I can go back in time or forward in time very quickly using the keyboard shortcuts. These tabs end up fully replacing the back/forwards feature built into the browser. Silly, right? Yet it works better.
Honestly, if someone asks me to flip to some task, it's usually about 3-4 seconds at most to get there, even with well in excess of a thousand open. When you're juggling a lot of tasks throughout the day for a multitude of clients and their clients, this shoots your productivity through the roof. 60-80 emails? 40 phonecalls? Oodles of tickets? No problem getting everything done. After all, all the tabs are up in front of you, waiting to go.
And if for some reason you brain-fart on where something is, now most web browsers have a tab search feature too. Takes a bit longer, but you can still get to the right tab in 10-15 seconds typically.
It's really work scenarios like this that drive this sort of need. When you're basically the helpdesk for multiple companies and other IT people and all their clients and their diverse tasks/requests. But I could see anyone that engages in heavy duty rabbit-hole research benefiting from similar UI use, perhaps with slightly less activity throughout the day, but still needing to keep tons of sites open and available until project completion. The difference there would be that they're working on a few larger projects, not dozens and dozens of smaller ones driven by clients.
I think most people that don't do this sort of hyper-tasking have no idea how proficient you can get at it. It's like those secretaries that pull off 200-300wpm on Dvorak or other keyboard layouts. Most of us are sitting in a more reasonable 30-60wpm range. Or those people that power-slide the lambo into a parking stall on a movie. It's way outside the realm of average use and skill, but you can't help but be impressed when you witness that proficiency.
Hyper-tasking is a skill that takes years to build up, as it requires mind, computer and software workspace to all be in sync with one another. But when you sit behind someone and watch them fielding requests and handling tasks that would normally take a team of 5 or 10 people, it's quite impressive.
Honestly, if I could have the perfect web browser for my use and my work, I'd happily pay $10/mo for it, forever - or at least until I retire. Why are pretty much all web browsers free, but don't cater to power user use cases like this? Hmm...
If you bothered to stick around until the end, I hope that explained one use case in a way that is understandable!