I think Carlisle was a problem there.
A part of being an effective leader is understanding your human inventory, playing to their strengths, and talking to them and treating them in an effective manner.
Carlisle clearly had a bit of a "my way or the highway" kind of approach. His treatment of Dennis Smith started to alienate Doncic....sometimes it's unavoidable, but the author of this article clearly thinks that Carlisle could have done a better job.
I can understand Doncic questioning Carlisle after his treatment, but my god, how can Doncic think it's ok to play himself into shape every year? That's just not going to work long term. Any older person knows that if you let yourself get out of shape, it gets harder and harder every year to get back into shape. Doncic's career will be stunted if he doesn't change.