A player is undersized his whole life, so he is expected to fail at every level he plays. Despite this, he works very hard and succeeds, at every level, culminating in a top 10 season in the NBA while leading a team that won 53 games.
He achieves this success on a team where the coach, widely considered a genius, is the unquestioned leader, management is among the best in the league, and the team is populated by overachieving, hard-working outcasts.
This player is then traded to a team full of veterans who couldn't care less about the regular season, many of whom have been highly regarded and well paid for most of their careers. This new team doesn't practice, and the coach is little more than a figurehead. The owner has a history of talking too much, and the GM is a rookie.
Most importantly, the whole franchise revolves around a superstar player who wants to dictate how absolutely everything is done including who is on the team and how his teammates play off him. Said superstar, in his fifteenth season, truly doesn't care about the regular season and this apathy trickles down to his teammates. The superstar has been the best or one of the best players in the league his whole career after being drafted #1 overall as a storied high school recruit; he has never known a time when he wasn't considered a big deal and expected to succeed beyond all others.
And we're surprised this player, Isaiah Thomas, isn't happy on his new team?