Here is what I think is happening--there isn't a source who is coming out and saying this publicly, but this is just reading the tea leaves and follows what big reporters (Windhorst, MacMahon) are tip-toeing around. I think Mitchell asked for a trade before the draft. He named MIA and NYK as his preferred destinations. However, both the Jazz and CAA want to keep this quiet.
If people know that Mitchell requested a trade, the fans will be furious with him. Kids will be crying and people will burn their Mitchell jerseys. The fans made a big backlash against Hayward when he left in free agency. Mitchell wants out with 3 years left on his deal. It's just going to be ugly for Mitchell and CAA doesn't want that. The league doesn't want that. It's just a bad look all around.
If Ainge abruptly trades Mitchell, then people can say the Jazz are going in a different direction. Mitchell can say he has nothing but love and gratitude for Salt Lake and the Jazz. (Same as Dejounte Murray.) If people are angry they can blame Ainge for changing the direction without giving Mitchell a chance to run the team. Ainge will say, "It's sometimes hard to swallow, but this is what's best to try to bring a championship to Utah."
Jazz have been actively discussing Mitchell trades with MIA and NYK for the past 10 days. Then when KD asked out of BRK last week, the Jazz inserted themselves into those discussions as the team that could facilitate by providing a young All Star as compensation for KD going out. So between MIA, NYK and now BRK, Ainge is making a market for Mitchell.
If the Jazz don't get the offer they want, they can hold onto Mitchell into next season and put on a happy face for the fans. They'll say, "We are building this team around Mitchell." Then they can try again to move him at the trade deadline or next offseason.