Because it is between absurdly rare and unprecedented for a sitting president running for a second term to not get the given the significant advantage an incumbent possesses. The party not standing by the practical and spiritual leader of the party would have been taken by most amaricans as surefire evidence that the party had discovered a scandal about his so massive and overwhelming it put everything Trump ever did to shame.

While the primaries were and are an excellent place to put pressure on the sitting president to actually do something, their outcome was a forgone conclusion unless Amarican voters cared a whole lot more about Palestine than they actually do, as that was the primary thing that changed between 2020 and 2024 where Biden’s perspective has an impact. Practically, the time to find a better candidate are 2019 and 2027, the mid presidency elections are a time to push the president to fulfill more campaign promises. Something that is more difficult when the legislature is controlled by obstructionists who are publicly committed to blocking everything they possibly can until they have complete control.