Perhaps Kyrie already told Ainge and Ainge has moved on but just hasn't graced us with that info? It sure appears Ainge is deep into plan C or D and so has moved on from Kyrie. I think Ainge may have moved on from Horford as well.
Or maybe Ainge found out through other means that Kyrie is gone and then moved on. The recruiting text stuff could be how he found out, though not sure on the veracity of that.
Or perhaps, Kyrie will do what Gordon Hayward tried to do, tell his old team that he will be leaving before officially letting his new team know he will be joining them. Remember, Hayward wanted to let Utah know but the info leaked out before he could do it. Everyone had figured for weeks that Hayward to Boston was a sure thing, but Hayward still didn't let Utah know until after he had an official sit down with Boston that he was leaving.
Yes, the situations are slightly different as Gordon was still listening to Utah's proposal but it shows that players do sometimes wait until after meeting with their new team before letting the old team know they are moving on.
I don't see that Kyrie not informing Ainge he won't be returning is any type of big deal or is a reason to lob further hate his way, especially when we don't know for sure that he hasn't already done so.
There is lots of reason for people to be angry with Kyrie:
* His poor leadership
* His terrible performance against Milwaukee in the playoffs
* Fighting against the Stevens' directions and coaching
* Being a major part of the team's poor chemistry this year
* His type of game(I don't get this one as so many that claimed they hated his game and fit were the same people that loved IT)
* He replaced the beloved Isaiah Thomas
* His quirky personality
But, this....this is no reason for consternation. He may already have told Ainge he is gone and it's also very common for players to not let their former teams know they aren't moving on until the player verbally commits to their new team in person anyway.