A competent technician with access to a workshop can make even 80 year old vehicles work. That is long past the service life of that vehicle but it can still be done, an iteration of the same technology is likely still in use today though in your car.
That isn't possible for software simply because reverse engineering is not simple, reverse engineering a small microcontrollers firmware might be possible, reverse engineering even something like old unix wouldn't be and definitely any modern operating system wouldn't be even though there is no legal precedent for that source code to be protected.
In 30-40 years time when early windows and early DOS copyright expires do you think Microsoft is going to benevolently make that source code available? It has legally become public domain but the source code will still remain closed.
How about firmware for IOT devices being installed in your house, it's likely that that hardware can be made to work for the next 60 years but you are forced to replace it in 3 when the manufacturer decices it's no longer financially viable to support it.
Is it "Here's a manual and a pile of tools, follow the instructions" hard?
Most maintenance on vehicles is exactly that.
The smart fridge that has a buffer overflow leading to RCE cannot be fixed quite a easily as as replacing the brakes on my car, neither is easy but one of those a monkey with a spanner could figure out eventually.
That isn't possible for software simply because reverse engineering is not simple, reverse engineering a small microcontrollers firmware might be possible, reverse engineering even something like old unix wouldn't be and definitely any modern operating system wouldn't be even though there is no legal precedent for that source code to be protected.
In 30-40 years time when early windows and early DOS copyright expires do you think Microsoft is going to benevolently make that source code available? It has legally become public domain but the source code will still remain closed.
How about firmware for IOT devices being installed in your house, it's likely that that hardware can be made to work for the next 60 years but you are forced to replace it in 3 when the manufacturer decices it's no longer financially viable to support it.