What happened with Paul Dini and Bruce Timm?

I realize this question is old hat. Other jobs come and go and people want to move on to different things. But considering the powerhouse Bruce and Paul were in the 90s...its so bizarre that the two of them haven't collaborated on a project together since Return of the Joker. I'm still surprised no one reached out to Paul to write the Batman/Harley Quinn movie...if anyone would be down for that it'd be Paul. And Paul has come back to DC /WB multiple times. He just wrapped the new DCAU comics with Alan Burnett.

At the very least does it seem like something's off. Paul's mentioned in interviews he's not happy with some creative decisions in Justice League? I can't even believe WB wouldn't try to reform the team that was such a winning formula for them for over a decade.