Why? What happened in 4 years that revealed to everyone beyond a doubt that it wasn’t legitimate?
Where I live, no one questions that the election was rigged. Most believe it was. I haven’t done enough of my own research to know one way or the other.
The key is that every single challenge has been debunked, often in court and often by Republican judges. When every challenge has been debunked, it's time to accept that the vote was fair.
The problem is that it's too easy to hallucinate new challenges. It's easy to claim some guy stuffed ballot boxes with no evidence, and if people want to believe that, they will unless given irrefutable proof to the contrary. But how do you prove irrefutably that Fidel Castro definitely did not stuff all the ballot boxes? Apparently, you can't.
Where I live, no one questions that the election was rigged. Most believe it was. I haven’t done enough of my own research to know one way or the other.