That's because he stopped being a character and started being Kurt's arm-candy who dresses like a flamboyant '50s Archie Andrews and gets all the solos.
Blaine wasn't a character at Dalton either. He was Kurt's Prince Charming with perfect hair, perfect uniform, perfect everything who just dropped from the heavens to serenade him.
Blaine has two modes. Perfect, charismatic put-together song-and-dance man, or fumbling goofball.
He's one of the most woefully underdeveloped characters on the show (so far this season he's been sliiiiightly better, but that's not saying much), romantically involved with one of the most developed.
And the most frustrating thing is they've tossed out these throwaway passing mentions of things that could easily give him more substantial storylines (his dad not liking he's gay, his past getting gay-bashed, etc.), and every so often they repeatedly allude to this underlying insecurity/angst he has, but they just never do more than scratch the barest surface.
Also....I will never understand why the wardrobe and makeup departments feel the need to inflict some of the things they've done to Darren Criss...it's like, do you go out of your way to eliminate any sliver of natural attractiveness he possesses?
Would it kill Blaine to at least occasionally look less like this:
And more like this?