Part of the problem is that blue team leaders systematically block more progressive candidates and policies (Jamaal Bowman is a prominent recent example). As a progressive voter, blue leaders are harming you by denying you the progressive candidate.
In a sense, this is something the blue team can afford to do only because they count on you voting blue anyway because the red team winning is even worse.
That's blackmail (or extortion, perhaps more accurately). And it's bad.