I'm not so sure that's true. You can rent a Skylake chip on Google Cloud that'll perform 1.6 trillion 64 bit operations per second for $0.96/hr preemptively. That's enough to run one instruction over a 64 bit address space exhaustively over 120 days, or for ~$2800.
Obviously that needs to be multiplied by the number of instructions a test needs to execute (and it has to be well written with AVX 512), but we're not talking nation state levels of resources here for simple cases, and that figure is only going to drop further with time.
Not to mention the potential for FPGA or ASIC implementations if the tests are important enough.
Hmm that's surprisingly within reach. I bet you could crowd-source that kind of verification with BOINC.