I assume you're playing glib because you're one of those Everyone Must Be Wrong But Me and Tuff Hockeyman Torts guys, but:
He needed the rest earlier in the season. Given his situation, they should have been managing his usage all season. Even just maintaining through the grind of an 82 game season would be tough for a guy who had missed nearly 2 years prior. Let alone a guy on the wrong side of 30 who basically had his spine rebuilt.
Prior to the All-Star break, he was averaging nearly 20 minutes (19:57) per night. And he was fresh and effective at that point, so Torts leaned on him like crazy: He played as many as 24+ minutes some games.
Much of this was around the time that Tortorella was scratching Frost—his decision, remember—and so Couturier was being forced to eat minutes because the Flyers already have bad center depth and were making that situation even worse for themselves by willingly sitting the only other top-6 caliber center option they have.
All that took its toll, and you could kinda see it happening in real time. Couturier's production and effectiveness dropped steadily. He has always been kinda slow, but looked slower than he used to be at the start of this season, and has looked even slower than that as the season has progressed.
So this is a situation Tortorella created for himself. He made lineup decisions that put more work on Couturier's plate than he should have been given. Rather than easing him back into the game or practicing any type of load management, he leaned on the player with hard minutes in order to secure those all-important early season wins for this so-called rebuilder, and once all that added up he cut his minutes and is now scratching him.
