The point isn't that 1 person can understand an entire smartphone silicon up. It's that 100% of a smartphone can be understood by people. A maths theorem that can only be partially understood/proven only has value as marketing collateral.
There are many problems that aren't "interesting" in a mathematical sense but can still have valuable proofs. The entire field of formal methods in software development is mostly about this kind of problem. If I want to be sure that no input can cause out-of-bounds memory access, or that my superoptimizer found the lowest possible cycle count, I don't care if it's elegant, I just need some machine-readable proof I can run through my trusted verifier.
If this is true, then what's really the point of math? A lot of math is actually useful. A proof regarding cryptography, for example, would have practical application even if not understandable by humans.