I think its pretty simple. The Celtics looked at the CBA and said "Its hard to build a contending team when your two best guys are taking up 70% of the cap and neither is an MVP level player. So since Jaylen's value is likely at its highest let's see if we can move him and restructure our team."
They then proceeded to shop him while maintaining a high asking price of 4+ first rounders, because if you aren't going to get a haul for him its not worth taking a step back next season when he still has 3 years left on his deal. As of now it appears there isn't a team willing to bite on that high asking price, but now the issue is Jaylen being shopped has gotten out and clearly it bothers him to some degree.
So the question now becomes: Do the Celtics feel like the relationship is so bad that they will accept 50 cents on the dollar? Or do they go to Jaylen, smooth things over, see what next year looks like and revisit things net summer if a now healthy Brown/Tatum pairing doesn't seem like it's enough?