I think one of the reasons the retro car thing is so huge in the USA is that the cars STILL EXIST on the road - there are (poor) people using ancient cars as daily drivers, so when the desire comes to find a retro vehicle, they're out there and available and cheap.
Not so much with old computers - NOBODY, not even the poor in the USA, are trying to make do with a 8086 as a daily computer. Phones and better computers are simply too cheap and available.
Are car licenses (whatever you want to call it) more lax in the US? In the UK it is more expensive running old cars because there's an annual "Ministry of Transport test" (which is broadly just referred to as "MOT") with really strict regulations. If your car fails it then it's not road legal.
I remember from my trips to America that even some of the well maintained cars there wouldn't have been legal in the UK. For example some didn't have orange indicators, instead using the red break lights as an indicator.
Most states actually make it CHEAPER to use an older car - for example, California does NOT require smog checks on cars made before 1975.
A very few states have a more stringent "inspection" but it mainly checks that the car has working lights and brakes - nothing like an actual costly check.
The USA doesn't even mandate daytime running lights as far as I know.
Some states also have 'classic' registration which (in WI at least) is paid once and lasts as long as you own the vehicle. It's more expensive up front than a regular yearly registration, but once it's done it's done. It also carries additional restrictions befitting the intended operation of a 'classic' (e.g., owner must also have a regularly registered vehicle, not allowed to drive in January, hauling restrictions if it's a truck) which make it cheaper only as a second vehicle.
The rules are designed to apply to vehicles being preserved, and are a help to hobbyists who can afford to own two or more cars. They seem to be designed - for better or worse - to exclude people who happen to rely on an older car as their only vehicle.
For example, I’m from Illinois, and you only have to have an emissions test in the Chicago and East St. Louis regions. I grew up near Peoria, where you can seemingly drive whatever disgusting uranium-and-coal-fired jalopy you want.
It depends on the state, some do annual emissions and/or safety inspections and require failed vehicles to get fixed. But a lot will just let you drive nearly anything.
Depends in the state and county. Some require both an emissions and safety check, but the safety is far less strict than the MOT. Some only require emissions testing. In some cases no testing is required at all, e.g. niche vehicles like motorcycles and conversion kits for SxS ATVs.
Not so much with old computers - NOBODY, not even the poor in the USA, are trying to make do with a 8086 as a daily computer. Phones and better computers are simply too cheap and available.