The problem is that voting machines are a competitive system sold to various levels of government. At the state level, there are different requirements, but not unified at the federal level [0]. Due to the differences, there cannot be a single mandated design, as the voting machine companies are not required to be consistent from state to state. There is lots of history here, which I haven't gotten very far into, but I think most would agree that reform and consistency would solve these problems. That wouldn't benefit the voting machine company profits though, so there is huge push-back.

[0] https://www.eac.gov/assets/1/Page/State%20Requirements%20and...