The fundamental difference is that obsolete computing hardware used to be difficult for owners and third parties to toy with only due to its inherent complexity, not from malicious intent. This difficulty could be overcome, both in theory and in practice, and with time and effort and a sufficiently persistent community (often reflecting the scale of adoption of the device in question) the difficult parts quite frequently would get overcome eventually.

Especially since the DMCA, there's been a huge increase in the efforts of companies to "secure" their products against "hacking" and tampering using sophisticated, often uncrackable encryption keys, reliance on remote always-online services which they provide for free (until they don't, because it's not like they thought about that during the product design and who could possibly expect them to support their products forever?!), and time-locked and sometimes even physically self-destructing components. These kind of designs now completely saturate the marketplace, and it's also become illegal to even try to unlock them, thanks to the provisions of the DMCA and the lack of any workable exemption for right-to-repair or abandoned products no longer commercially viable.

Nobody expects a company to have to support their product forever. Of course that's unreasonable. But it is reasonable to expect them not to design things that intentionally turn into e-waste the moment they stop supporting them. It is entirely reasonable to expect them to design an end-of-commercial-life strategy for the products they develop and sell. This is why copyrights that are allowed to expire become public domain instead of having all the books with expired copyrights burned. Because we, as a civilization, chose to have that happen, and we made it part of the copyright laws. Why do we allow electronics to remain proprietary and encrypted when they are no longer profitable? Why not require them to be opened to the public domain too? Would this not be in society's best interests? It would not be in the interest of the companies interested in planned obsolescence, that's for sure, but maybe it's time to stop letting them decide. They have not been kind to us. Stop being kind to them.