> Software doesn't have this scarcity dynamic

Time is finite. People’s problems that can be solved by software is also finite. There’s diminishing returns in improving software. Rewriting bash in rust, and then testing the result would barely help anyone. Also the real world (where inputs come from) is messy. You can have the perfect mechanism (memory safety), but that grain of sand (corrupted or unexpected data) can still make it behave erratically (wrong result).