Nothing is more important to Republicans than controlling the WH, perceived to be their ‘birthright.’
And just as important is controlling the WH for as long as possible – preferably eight years; much of the consternation at Trump’s loss this year is that Republicans were ‘cheated’ out of eight years of Republican rule.
But if elected in 2024, Trump would be able to serve only one four-year term – Republicans wouldn’t have the incumbent advantage going into the 2028 election year.
It's not hard at all to see why Rump would
want to run in 24 --- pure ego, so he could give himself a chance to deny that 2020 ever happened --- but why the Party would allow it to happen, that's a head scratcher. On the other hand, it was the same head scratcher as to why they allowed it in '16, so the ways of the irrational are by definition unpredictable.