there’s no _coup_ (not coop) because primary processes are not part of the constitution. candidates can step down (as biden did for the good of the country, and LBJ had done before him). there was no real choice to not pick biden, either, as the incumbent.
the party will now have an open nomination process where delegates will pledge based on how people of their state best want, and keep in mind that most americans did not want biden OR trump, so they really are doing what is best in the interest of american democracy
compare this to the RNC and GOP which has done nothing but embrace one criminal authoritarian crook for the last decade, and you’ll see why your comment doesn’t really make sense.