2) They still want people to root for Klaine, and showing just how much Blaine's actions devastated Kurt is going to make a Klaine reunion really unappealing.
A more effective way to make people root for Klaine again is to start over from scratch after some time has passed. The proposal along with all the scenes of emo!Blaine only served to make him look immature and desperate. As for Kurt, he's written as almost a non-entity in this breakup even though he's half of Klaine.
Not developing Kurt/Adam and going all the way with Blam is a mistake imo. Kurt and Blaine don't have to be tied together for the rest of Glee. Having other well-written, established, alternative "ships" for each makes for good television once Klaine 2.0 rolls around and makes fans swoon again.
They want Klaine in limbo and dancing around each other.
It doesn't even feel like that. There's no suspense or uncertainty. They want these two tying each other down and it's not a matter of will they get back together, it's when. As a result, all their drama feels like a contrived waste of time. Same goes for Finchel, but at least Rachel has Funny Girl/theater girl problems going for her and Finn is Harlem Shaking in college.