I'm also not buying the "move to Vegas" conspiracy theories. I think some variation of this is how it played out based on everything I've read (which has been way too much).
1. Nico and Luka clashed and potentially didn't like each other. Luka probably did take advantage of his superstar status (as most probably do) and had his own personal medical team, etc. involved, and yes, did have documented issues as far as conditioning, dealing with refs, drinking, etc. (not unlike Nash and Dirk at that age who I saw out all the time during that era).
2. Nico and new ownership didn't really help the above dynamic by running off long time Mavs support staff that Luka had good relationships with.
3. Nico's surrounded himself with "Yes" men in the front office.
4. Nico's background is AAU driven/U.S. basketball and he's not as comfortable with European influence/European star player.
5. Nico had a longstanding (going back to high school) personal relationship Anthony Davis, and considering all of the above, believed AD to be a much more comfortable "fit" for him and what he envisions for the Mavs. It was always AD or bust for him regardless of reports to the contrary. Lakers able to take advantage of this.
6. There was zero regard for state of franchise post the Kyrie/AD window. Nico has no desire to still have this position once Mavs are in full rebuild.
7. So given the above, Nico convinced himself (without anyone providing strong opposition) that this was in fact a good basketball move. Dumont is fucking clueless about basketball in all aspects and allowed himself to be convinced by Nico that this was a good move.
8. Nico and new ownership aren't from Dallas, have zero appreciation for Mavs history and Dirk in particular. They had no idea what the quote on his statue said and no appreciation for how much the 2 way "loyalty" with Dirk meant to all during the era of star players bouncing around and teaming up together, and thus no appreciation that Luka was, to this fanbase, the more talented heir apparent. Thus, they completely underestimated the fan backlash.
9. Cuban had been frozen out and had no real opportunity to save these idiots from themselves.
10. The entire organization, after completely under appreciating the fan backlash and not expecting the almost universal assessment that this was, in fact, an absolutely retarded basketball move, has managed this from a PR perspective about as bad a humanly possible.