I think for a lot of people, just a lot of trouble to do that. Plus there are primaries, and midterms. I know I would never register and re-register like that.
OK
Remember primaries are little more than popularity contest and are still subject to the “smoky backroom” caucusing that took place (Tamany Hall chose FDR).
Just ask Bernie Sanders.
They do not place anyone in office.
I, personally, find them unConstitutional.
They are not election.
Lincoln was chosen using the “party caucus” method.
So, in the long run, you should only have to re-register every 2 years.