If the Axis had been dropping 1000+ tons of bombs on American industry every day, then maybe that would have been rational.
Similar if the Axis had large-scale resistance forces operating in America, able to sustain at-scale acts of industrial sabotage.
But the Axis already knew that America had a huge copper industry. With no way to affect that industry, at scale - long lists of American copper mines, refining facilities, factories, etc. were no more valuable to the Axis than collections of apple pie recipes.
The bearing plants didn't have much of a long term impact if I recall...
The oil campaign OTOH, worked out well.
I'd guess actually going after stuff like wire/brass casing production, while it could have an impact, the 'ROI' is likely lower than more important logistics meta-targets (i.e. oil and gas production and transport infra/equip) and those are far easier to 're-boot-strap', one can theoretically draw copper wire from their garage with a reasonable base starting piece and draw jig/rig.
Also, like bearings, it's easier to 'surplus'. Surplus Oil sitting in a field or penetrable location? Obvious easy pickings. Stockpiled wire? I mean you could but frankly even if you burned/melted all the wires someone can just collect it and re-make wire. It's not like oil where the resource gets completely destroyed in the process.
There wasn't much of a Nazi spy presence in the US much less effective saboteur operations. One of the few people convicted for espionage had their conviction overturned because the information they passed was publicly available. The US was never under much direct threat, there were a smattering of attacks and raids on the West Coast but those didn't amount to much. Extreme distance was a better shield than any secrecy or military might, it's part of why the post war years were so good and continued for decades afterwards, the US was completely untouched and the rest of the (then) modern world was bombed to absolute smithereens.
Isn’t this exactly what should be looked into? Find weak point and hit them. Germanys ball bearing plants and oil refineries got targeted this way.