Trump refusing to accept the 2020 election results should've been the line for many voters, but sadly it wasn't. And the potential crimes he and some of his allies may have committed while trying to overturn it will now never be prosecuted.
2020: > More than 158 million votes were cast in the election
So 3 millions of Democrats suddenly decided to not go out to vote "to save democracy" against "fascism"?
I saw many people close to me not bother voting because they didn’t enjoy Biden’s presidency, despite voting for him in 2020.
So, I find that FAR more likely as a reason than supposed election fraud.
(I still argue with Pizzagate adherents on a monthly basis. They think it's perfectly logical.)
You answered your own question. Voting was made more difficult in 2024, so fewer votes were cast.