There are far far too many links in that massive chain to trust on obscurity as security.
Furthermore it's not just obscurity it's also the other things I mentioned non-connectedness being one of the biggest.
I'm not sure how you can argue that obscurity is a strong method of security when one machine in the country could be compromised, or the counting method code could be compromised, or the programmer verifying the code could be compromised, or the distribution system of voting machines could be compromised, or any part inside the voting machines could be compromised (e.g. the touch interface), or the voting machine remains secure during the voting period (i.e. voters are tampering with it on poll day).
All machines are hackable all systems are hackable. But focusing on the box showing you can hack that changes absolutely nothing about the overall threat of the US election being hacked. No one with serious technical understanding would claim that it was impossible to hack the boxes. And so you are back to a much harder task which is the social engineering part of convincing thousands of people to betray their country and no one finding out.
Then why use machines at all? As mentioned in this thread multiple times, Germany can count all votes within a few hours without any voting machines.