[duskwuff]

I think you're overestimating developer ability/willingness. There's a lot of hardware out there which could in theory have third-party firmware built for it, but which hasn't because it's just too niche for anyone to have bothered, or because there's insufficient public documentation.

Most smart TVs, for example, fall into both categories. There are simply too many models for a third-party firmware effort to take off, and documentation on the hardware used in these TVs is usually nonexistent. (And the hardware is often already stretched to its limits on the stock firmware -- implementing "new functions, including codecs" is likely to be impossible.)

[grishka]

There are many models of smart TVs, but they reuse components and software a lot. I remember rooting my Samsung TV with a universal exploit that worked across something like several years of models.

[wizzwizz4]

I think you're underestimating the tenacity of hobbyists. Some people hack every device they own, then release the software they wrote to do so; it only takes one or two of these people to write the drivers for a few dozen devices, and then they all run Debian.