PCs can last decades.

They can, but how much of that longevity is in your control? My last round of Intel NUCs all died within a month of each other at 4.5 years of age - I have NUCs that I ran for 6 years before them that still work fine, but that's now 11 year old hardware and remarkably underpowered compared to today's options...

People in the US would just hoard used components.

Some would, some already do. Most?

And piracy still exists even though there was real effort to end it.

How real? Piracy still exists because it was too politically costly to end it.

I guess the jailbreaking/right-to-repair community would eventually get around the limitations.

They already do for the current limitations. How big is that community vs the broad market?

black markets always won.

Did they? When I traveled through the former East Germany in 1990 my bicycle was 40 years of design above and beyond anything any East German had seen before. I stayed with a "wealthy" retiree in his apartment filled with the latest/greatest of what he could obtain on that black market: a reel-to-reel tape player, a 9" color TV, basic Hi Fi gear - nothing resembling a computer.

The firearm situation is a bit exceptional

Thankfully.