When Monte McNair acquired the draft rights to Sasha the Kings were coming off a 30 win season and had just hired their 12th head coach in 16 years. In that context you're trying anything to add talent to the roster and see who sticks.
By the time Sasha actually signed his contract with the Kings a year later they were a 48 win team coming off a hard-fought 7 game playoff series loss to the Warriors. Roles were established, expectations were high, and there wasn't an opportunity to bring the new guys up to speed slowly because our schedule was front-loaded with 3 "prove-it" games against the Warriors in the first month not to mention the in-season tournament games in November and December.
I don't think Mike Brown had a problem with Vezenkov, he just had other priorities. Maybe Vezenkov took it too personally? I'm not sure what his expectations were. Barnes and Lyles getting re-signed already made it so he would have an uphill battle to establish rotation minutes and Coach Brown prioritizing defense this year didn't work out in Vezenkov's favor either. It's kind of odd for a guy who has played in only 42 NBA games to say "I don't like my role, trade me out of here". Now the impression is out there, accurate or not, that he's a me-first player who cares more about getting his minutes than team success. I don't think that helps trade value so if his goal is to get traded, he just sabotaged himself by going public with a trade demand.