Republicans aren’t as organized as Democrats. Republicans include: social conservatives, economic libertarians and populists, among others. Uniting all these people is something of a trick.
As to Trump’s megadonors, I don’t know that there are any. Trump relies on MAGA donors, not megadonors. Thousands, even millions of small donors. In 2016, Trump’s vast army - much of which was “under the radar” - propelled him to victory in the key states determining that year’s outcome. In 2020, not so much. The polls had Trump down by 7 points, but Trump rallied his army, both seen and unseen, and lost by only four points. More significantly, he lost by only point in each of the three states that made the difference.
More precisely, Trump lost by 4.5 points in the popular vote, while the Republican congressional candidates lost by 3.1 points. If Trump had lost by 3.1 points in the popular vote, he would have been re-elected President. Unfortunately, the Republicans weren’t very united that year. The Republicans mostly came together in 2016, and didn’t come together enough in 2020.
Conservatives are individualists, Liberals are collectivists. Conservatives have their own lives, and families to take care of, and see government as just a necessary evil. Liberals see government as the solution for all of the world's problems and they center their lives around it.