I think maybe on some level the right simply can't/don't believe that Joe Biden (a man who they think is bat sh*t crazy senile), actually beat trump (who they think is the greatest thing since sliced bread) legitimately.... of course they DID have a little help being lead to the conclusion that it was "stolen".....
So in their mind, Joe Biden is illegitimate.
This is basically the same thing Trump tried to do to Obama (with the whole "birther" birth certificate thing)... Obama couldn't be legit if he "lied about being born here". Biden can't be legit if he "stole the election".
The right doesn't care about experts, reports, facts, news, etc... To them Biden can never win. Anything against trump is "fake news".