Because it's 4-on-5 on D every time Sexton is on the court. He looks like he's hustling, but none of it's beneficial to preventing the opponent from scoring.
On offense he believes he's the superstar player of the team and no-one else should touch the ball. This goes for JC as well, but everyone agrees that that's just who he is. Everyone else was just standing as wallflowers on O the whole quarter while Sexton and JC took turns pounding 20 secs off the shot clock and putting up some random **** or throwing a last second grenade to a teammate. When everyone else is completely disengaged on offense, this leaks into the D as well and it's hard to be as into it.
The Jazz had a real shot when they were up 9, 7, 5 pts.
This was one of the most mind-boggling plays of the whole NBA season. Down by 2, first take off half the shot clock. Then go before the screen is set, then go again before the screen is set, lose the ball - game over. And of course play with blinders on, so even if he hadn't lost it, it's a 1-on-3 Sexton against Lyles, Huerter and Murray.