Depends on the hardware codecs use case, as some legacy cards are valuable to people that own legacy workflows.
Without CUDA + hardware-encoders a GPU is just a paperweight regardless of age for some use-cases. =3
You've repeated this FUD about DKMS breaking, but it's exclusively a rolling-release issue. And even then you can still fix it, tons of places will containerize their workload and dump it into a proxmox:latest instance.
It is not FUD, but rather the consequences of out-of-band proprietary mystery blobs, dependency injection, and major structural changes within the kernel or user space programs. Many legacy dkms simply don't survive the code permutations over the long term (usually Wifi cards, equipment, and GPUs.) Thus, projects relying on such drivers break eventually as people start to abandon the legacy platforms.
Linux is good at many things, but LTS only slows the compatibility decay cycle to years instead of weeks. The several thousand tonnes of waste hardware it turns into garbage, and locked offline Application licenses do matter to some folks. It is the hidden Spiral development liability in most FOSS projects. =3
Windows Service Packs do the same thing. Install Windows 10 software on a Windows 7 machine and you'll end up with a similarly-bricked system.
Abandonware popularity is a relatively recent phenomenon, as hardware became cheap enough to be disposable... and SaaS/DRM hit the entertainment industry.
Most people are not going to port AAA title dependencies to ancient hardware, but the "Doom will run" on just about anything meme is usually still true. =3
I'm not sure what the state of the open-source drivers is for the really old nvidia GPUs, but for Pascal and such it's pretty decent. No video hwaccel though. However, for hardware encoding, NVENC has improved a lot over the generations. So the old chunkers are probably beat on every metric by e.g. a T400 card. Or Intel Arc (business model: "Quick sync for AMD").