Because the supreme court judge has decreed that the voting machines are UNQUESTIONABLE. That's all there is to it. Not even our elected representatives get to doubt these things:
Fun fact: brazilians commonly express feelings of superiority towards civilized developed world nations because of these voting machines. They think americans, germans and everyone else in the world are living in the literal stone age due to their "archaic" voting processes just because it takes time to count the votes.
How can a closed system that cannot be audited be considered trustworthy? After the voting happens, there's no physical proof of the vote.
Highly recommend reading this: https://dfaranha.github.io/project/evoting/