AMEN. This is basically true in every Democratic primary. Hillary Clinton's favorability among Democrats in June 2008 - after losing the most brutal, interminable, closely fought primary of my lifetime - was 74%.
Obama's? Also 74%.
One thing that will not be reflected On Here regarding the 2028 Democratic primary, where things will be highly factionalized and negative, but that will almost certainly be true in real life — most primary voters will have a favorable view of several (or even most) candidates once they get to know them.
Their allegiance to one candidate may be rather fickle/fleeting from one month to the next depending on debates, developments in the race, etc. Not to mention the strong possibility of strategic voting based on who they deem to be viable.
On the flip side, 15-20 serious candidates running will be overwhelming to many voters, and they will also be looking for any and all heuristics to narrow down the list in their mind.