I know Carmen didn't have much of a reason to return as Carmen Sandiego 2 years after The Dark Red Caper but I theorize that another reason it took her a while was because of the PTSD she suffered from.
Everything she did to Zack, Ivy, Gray, Julia, Chase, Shadowsan as Dark Red Carmen all comes back to haunt her and for the longest time she felt unworthy to be Carmen Sandiego and refused to even go near the hat and coat.
Maybe sometimes she feels she starts slipping back into Dark Red Carmen, like she finds it easier to lose her temper and feels guilty and questions if she really has changed...
Headcanon that while travelling around on capers and staying in nice residencies, the vile team like to meet up and have karaoke nights
Crackle, El Topo and Le Chevre are for sure the ones who are always on the stage. They are a mighty trio and sing their souls out like they're performing at a concert.
Carmen definitely likes to sit and watch but will once in a while get up to sing especially when they do group songs
Sheena says she hates it but when she's singing, she's PERFORMING (she can't sing)