It depends on how you see those devices. On one hand it's a block of hardware (like an appliance) on the other hand it's a CPU and RAM and storage etc. This is a weird gradient where the same could be said for routers (and we kind-of do that), but also for Smart TV's (which are left out in the cold, generally), and other devices with smarts in them (or: a CPU, memory and storage).

The general problem lies with the utility for mass-market products, even if you re-purpose it, how widely spread can you do that? How feasible are most ideas on what to do with products that are end-of-life? A lot of existing things are just dumped and forgotten about like thin clients, settopboxes (same hardware as Raspberry Pis) and entertainment systems in cars.

We like to point at manufacturers and products from well known brands but in reality it applies on a much larger scale, yet the infeasibility scales with it all the same. Some of it might be due to legitimate PKI-based lockouts, while other reasons might simply be the lack of broad interest and governmental policy.

In an ideal world the specifications on how the devices work and end-of-life disablement of lockouts would be a reasonable bar to set; it'd be hard to argue that it's bad for commerce, and implementation-wise even PKI-based systems have easy ways to facilitate this. The cost would be enablement from the manufacturer's side and for some brands the connection between their brand name and a device they cannot control the presentation of. I don't know how to solve that but it's definitely a much larger problem than people in tech might think of.