Question, if you were a Democratic Governor and your State was in play for this election especially since Joe bombed the debate and you were a candidate to replace Joe, would you want Trump to win? Trump would only be President four years, it appears to be late to get Joe off the ballot, so what to do? If one of the other potential Joe replacements won, well there go eight years. So is the best plan to not help Joe and wait until 2028?
Your analysis is correct.
That is why the governors did not challenge Biden in the primaries.
The downside to that approach is that it will be a crowded field in 2028. The first to strike against Biden would have had only one opponent to fight off....