Decommissioned hardware that is put in storage inevitably walks home with an enterprising employee to whom the risks from the business perspective are simply not a factor.
I just upgraded my 10 year old laptop because I wanted to do AI Art locally.
I ran video games, CAD, cellphone emulators, my programs, etc... on this computer and it still works. Heck, I still use it in a different room now.
Its not the 2000s anymore, we don't need tons of processing power to open web browsers and M$ Office. Decommissioning could be a rare event in the future.
Even if the standard consumer stuff works fine, all the annoying enterprise security and remote management software that you're required to deploy just seems to suck up more and more resources every year. Unless you're lucky enough to work in an industry where that sort of thing isn't needed...
But even if you forget the software side, most office workers don't take great care of their devices. Even a solid ThinkPad will often have bits falling off it after that amount of time.
As to bloat and performance, the standard amount of RAM in a laptop has barely budged in over 10 years. In 2012, a typical consumer laptop might have had 8G RAM and the higher end models 16G RAM.
In 2023, a quick search shows basic home laptops still for sale with 4G RAM, and typical consumer laptops around the $1000 price mark come with 16G RAM as standard.
CPU performance has increased a bit in that time, but not by a whole lot, especially single-threaded. An old laptop might be a bit slow, but it's usually RAM and operating system support which makes it obsolescent. Apps and web pages either fit in memory or they don't; the OS you're running either supports the latest app / browser (and thus web pages) or it doesn't.
Also it's not the useability it's the manufacturing warranty that goes with it. Personal use is a very different thing from business risk.