Why aren't the NSA and "crime actors" stealing my bank accounts and my crypto?
Because it would be noticed. We can't make anything tamper-proof (except possibly with quantum tech), but we can put in procedures and checks to make sure we would notice if our votes were discarded or flipped. Starting with the ability of each voter to audit how their votes were tabulated.
it would be noticed.
You mean it _could_ be noticed _if_ someone was looking.
We now know there are _many_ jurisdictions, including whole states, where the policy is don't look, don't ask, and don't tell.
It is the combination of tech frackery _and_ corrupt vote counters and recounters that are the problem.
You cannot have an honest system with dishonest people--every institution throughout human history has had to learn that one the hard way.