So cars ARE designed for robots. Really.
Thing is, they're designed for assembly.
They're made on an assembly line, put together layer by layer with the inner parts going in first and outer parts later.
I remember reading about one assembly line where it was designed so the engine came into the car from underneath.
For example, I had to get in the trunk of my car once to replace a tail light. I had to remove a panel, and it had a fastener that looked like a christmas tree. It was really hard to get the panel off, but when I was done, just position it and push and it goes click click right into place.
So I think they're optimizing for a car that assembles quickly and cheaply, and is reliable enough so it doesn't have to come apart.
"reliable enough" might change with electric cars though, because it's looking like they will have a fraction of the moving parts and may last 5x or more what an ICE car will last.
If YOU will take them apart, get an old car. They less reliable so they were designed for people to work on them. Get one of those. Better yet, an old pre-electronics tractor. They were designed for farmers to work on with a small assortment of parts.
Or get a Humvee. The first one, the H1. They were designed to be taken apart and fixed in the field, with a small assortment of tools and lives depended on this capability.