While I kind of understand the allure of messing with idiots, I think it's also a waste of time.
It's completely counterproductive to make angry people even more angry.

This is just my very biased opinion but if somebody has a US-american accent I immediately respect them less lol. It's an instinct.

When you have enough personal info about a population you can engineer advertisement so effectively that you can convince that population of almost everything. See Brexit.

There are probably two reasons:

1. It wouldn't change how the public thinks about them. People wouldn't understand how voting machines work, even if they were open source. Do you expect normal people to look at and understand code? Also people who have lost hope in democracy and want to believe that the election was a hoax will continue to do so anyway.

2. It's probably more comfortable for the manufacturers of those machines to keep them closed source. Why would they show the world how they work? That would disclose potential flaws which is bad for their reputation. And it would make it easier for competition to emerge.

p.s. I agree that voting machines are bollocks.