Auto engineers aren’t as evil as all that. They don’t design things to be difficult to service, but they don’t design them to be easy, either. Servicing what they build is simply not part of the set of goals. They work toward goals like:
Is it impossible to assemble it wrong?
Will it fail within warranty? (and cost us money)
Can we build it cheaply enough to make money selling it to GM?
If we build it at a loss, can we make it up by inflating the price of the replacement part?
Will I escape getting fired for designing a part that fails?
Can I cut down the number of assemblers needed to build it?
Once I design it, can I go back and save a few pennies with a small change?
In Ralph124c’s seat bolt mystery, the 6 bolts on the back were installed by a guy in the trunk (and he may have used the same bolt on other things in the trunk.) The other two were installed by somebody else inside the cabin, who may have used the same Torx bolts on the seatbelt anchors.
The decision was about assembly, not disassembly.
The bulbs were soldered into the circuit board because it’s cheaper that way. They made a fail-safe connection to the bulbs, and probably thought the bulbs would last forever (or at least until the end of the warranty.)
Seeing who posed this question, I suppose you mean the Tucker. 
However, the early Ford Mustangs supposedly were put together simply, so that a small number of tools were needed to work on it. That company is limping along on the edge of collapse. :smack: