It's all about timing. In 2020, we were in the middle of the worst public health crisis of our lifetimes. The whole country was shut down due to Covid and the president wasn't taking it seriously - denying that it was real, making jokes about it, blaming it on everyone else and wondering whether it would be helpful if everyone injected themselves with disinfectant. His complete incompetence and stupidity made past non-voters want to vote for him in hopes that they they could get their lives back to normal again. There was no such crisis this time around, so non-voters went back to being non-voters again.