I wouldn't worry about Kupp's snaps because the Rams were using two TE sets to beat Plantation Pete. Kupp was very productive with the little action he saw. He's Goff's favourite target so I doubt he's going to be phased out of the offense any time soon.
Gerald Everett has been injured the past two games, which explains Higbee's rise to prominence, though you're right that they went tight end heavy. As for Kupp, so far I found this, but it doesn't contain a logical explanation for his demotion. Why not demote Josh Reynolds rather than Cooper??? Kupp only played 29% of the snaps, even less than Brandin Cooks.
Rams snap counts: Cooks and Kupp barely play vs. Seahawks
The Rams came out on Sunday night against the Seattle Seahawks and punched them square in the mouth. Seattle had no answer for Los Angeles’ offense and could do nothing against the Rams’ stout defense, which has allowed just one offensive touchdown in the last two games.
It was a statement victory for the Rams, who had only beaten one team above .500 prior to this week. It also kept them squarely in the playoff hunt, only one game behind the Vikings for the No. 6 seed in the NFC.
The Rams got it done in a different way Sunday night, though. Rather than featuring their three starting receivers heavily on offense, Sean McVay went with more of a heavy approach, utilizing his tight ends.
Here are the offensive snap counts, which gives a glimpse at how the Rams got it done.
Offense
What stands out most is the fact that Brandin Cooks only played 27 snaps and Cooper Kupp played just 20. Combined, their 47 snaps would’ve accounted for about two-thirds of the Rams’ plays. Cooks didn’t have a single catch and Kupp caught four for 45 yards and one touchdown.
Josh Reynolds played just one fewer snap than Kupp and Cooks combined, and while he didn’t have a reception, he carried it three times for 29 yards and was solid as a blocker. Robert Woods unsurprisingly played all but one snap on Sunday.
Tyler Higbee and Johnny Mundt were a big part of the game plan. Higbee caught seven passes for a career-high 116 yards, while Mundt was utilized more as a blocker and succeeded in that role.
Todd Gurley played 80% of the snaps with only Malcolm Brown spelling him, not Darrell Henderson. Brown subbed in for the 14 plays that Gurley missed, carrying it five times for 21 yards and a touchdown.
https://theramswire.usatoday.com/2019/12/09/nfl-rams-snap-counts-seahawks-week-14/