In the latest Wrestling Wrestling Observer, Dave Meltzer has revealed that CM Punk's agent did recently try to open a dialogue with WWE. That presumably would have opened the door to the former WWE Champion stepping back into the ring for the company, but Vince McMahon as reportedly labelled Punk as the "one man I just can't do business with."
It sounds like no one in WWE, including Paul Heyman, have pushed for him to change his mind...probably because they know it won't make any sort of difference!
WWE stopped mentioning the fact Punk is part of WWE Backstage a while ago, and clearly don't appreciate what he's said about the company either there or on social media. The company only really agreed to let FOX hire him to keep the network sweet, and it sounds like a lot of interest in Punk died down when his big return came on a studio show pretty much no one watches instead of at a big WWE show.
For now, there's clearly no interest in Punk from WWE (which is a huge mistake as he could really help with those poor ratings), so here's hoping he makes his in-ring return elsewhere. All Elite Wrestling, perhaps?