The problem with old HW support is that the hardware is fine, the drivers are available and fine, but the kernel people decided to throw them out and replace by newer drivers which can run only newer HW products. Developers/vendors could be more user-friendly and keep support for the older hardware since the older compatible drivers exist, but they often don't.
What are these drivers you're talking about? Linux very rarely drops support for older hardware.
Things I remember off the top of my head in recent years: floppy boot support being removed, pre-ATAPI Matsushita CD-ROM support being removed, stuff like that. Turns out... you aren't going to be running modern Linux on systems that ancient anyway, because the minimum system requirements for just the kernel alone are already higher than machines of that era. So the number of people impacted by those cleanups should be ~0. Are you seeing drivers actively being used by people on modern kernel versions being removed?
You mentioned GPUs, but Nouveau supposedly supports Nvidia GPUs all the way back to the Riva TNT2 from 1998, and the Radeon driver should go all the way back to the original Radeon R100 from 2000. What are these unsupported GPUs you speak of?
Same with RAID cards; I see the driver for the Promise PDC20277 is still in mainline, and that's a PATA card from 2001 or thereabouts.
You can't endlessly upgrade software on ancient hardware; at some point the software outgrows it. Linux has historically been extremely good at keeping compatibility for old hardware, 20 years down the line. No other OS does that. But at some point things do have to go. I don't remember any time Linux broke something within a timeline similar to other OSes' support period.
1) dropping support of some Adaptec RAID cards in RHEL/Centos 8 with Linux 4.18. Like <= 5xxx series. Yeah, Adaptec 5x series is old and weak performance, but perfectly fine and widespread SATA controller card for servers. Many storage-oriented servers don't need anything faster.
2) Radeon RX4xx RX5xx GPUs worked on kernel 4.19, but they don't work for many people on newer kernels such as 5.10 and higher. Lots of error messages in dmesg, lots of reporting on forums, no official guide as to how to fix that. Amdgpu driver is in state of being endlessly rewritten presumably due to shiny new GPU cards and cutting edge Linux can't work with older cards reliably anymore.
The problem with old HW support is that the hardware is fine, the drivers are available and fine, but the kernel people decided to throw them out and replace by newer drivers which can run only newer HW products. Developers/vendors could be more user-friendly and keep support for the older hardware since the older compatible drivers exist, but they often don't.