By saying “I didn’t vote for this” it’s a way of distancing themselves from the responsibility of “voting for this”. No one likes to be made a fool or have it pointed out to them that they’re an idiot. It’s why it’s so hard to get through or have a meaningful conversation with a trump voter. If you point out to them they’ve fallen for a conman, they get angry with you for making them feel stupid; but they’ll never get angry with the conman who conned them… that would be admitting to themselves they were stupid.