Because Chychrun has played on his right side in the NHL, and Chabot hasn't.
Chabot is getting 2+ more minutes per game because he's their preferred option.
Chychrun was playing his natural side for a lot of the year, he was still being played less.
Chych has 16 games with at least 23 minutes played this season, he's played 47 games, half of which Chabot wasn't in the lineup. 34% of his games. 8 games under 20 minutes. With Chabot out of the lineup the first time, he averaged 25:51 a game. Since he returned, he's averaging 21:30, Chabot is at 24.
Chabot has 17 games with at least 23 minutes played this season, he's played 25 games, all of which had both Sanderson and Chychrun in the lineup. 68% of his games. 0 games under 20 minutes.
One is being leaned on more than the other, whether we agree it's the right decision or not is a different story.