Because 2-3 options means that whoever wins will need to endure weeks of costly campaigning on a last minute primary and receiving potentially devastating attacks and bad vibes from their own party immediately before entering the general against Trump. It’s suicide
Rules: candidates must have demonstrated national party support to enter the race and must not attack other candidates. 3 weeks of a massive amount of earned media — no need to spend money, journalists will be falling over themselves to interview them. Trump would be sidelined the whole time.
None of the people who have eyes on 2028 are going to risk this. Harris is the only one with access to the infrastructure that has already been built (and which takes *years* to build). Whitmer, Moore, Shapiro, etc., are ambitious, not stupid.