Quick Question: Subframe connectors- WHY didn't they do this from the factory?

Blame it on Nash, they started this unibody crap back in the 40's. Anyway you can shave materials and assembly time off of a mass produced product profits will increase.
These cars were designed to run skinny little bias ply tires so the body didn't have to be that stiff, and were certainly not designed to last 30 plus years.