It is 2022. Why do we only have one paste buffer?

What are you talking about? X Windows has three¹: CLIPBOARD, PRIMARY, and SECONDARY.

https://www.x.org/releases/X11R7.6/doc/xorg-docs/specs/ICCCM...

Note the copyright dates on that document.

¹ Actually, there are as many as you care to implement. These three are simply conventional; applications are free to use other names to identify other communication channels.

LCD: Least Common Denominator.

We're barely getting to the point where most people understand what you mean when you say "Copy and Paste that sentence" or "Right-click and select Save As".

Most popular software is going to be catering to the LCD for a long-time.

Not sure about the environment we are talking right now, but vim has 26 letter-,10 number- and 4 special-registers.

Oh, and ofc it can do a lot more with them than just using them as paste-buffers (use in macro, append-to-register, use in scripts, ...)

Who's "we" here?

https://www.brianstorti.com/vim-registers/

CopyClip is a great tool that solves this for macOS: https://fiplab.com/apps/copyclip-for-mac

the IDE I use (Qt Creator) has a past buffer history accessible with ctrl-shift-v, very useful

I used to have a tray application on Windows that keeps a history of what gets cut.