The system is made up of many components, and voting machines are but one part. Even though they might be hackable in various ways, there are much more efficient ways these days to sway an election. The Cambridge Analytics scandal proved one efficient way, while there’s now a growing belief that whoever controls the social media algorithm effectively controls public opinion.
And don’t get me started on the two-party-system in the US…

So no need to hack the machines, really. The system is flawed/corrupt elsewhere more severely.