I'm not sure if SUP is dying , maybe slowing.
Reasons IMO......
New boards are quite expensive for someone new to the sport so that scares off some people into trying the sport for the first time. 2 - 3 K plus paddle.
Retailers such as the Surfboard Warehouse used to flood the market with cheaper boards across a range of sizes which allowed many people to get into the sport with a paddle for less than the price of a big brand board. Since Tim left SBW the sup range has all but dried up which left a big hole in the market for newcomers.
Guys who know what they want in a board will always go to the bigger brands to achieve the performance style they are chasing.
Local SUP shapers have all but disappeared up here on the Goldy except for DEEP and Phantom. Many of the old crew from this site used to froth over a post from someone who had a locally made shape but they too are rare as these days.
I also think Foiling and Dinging is pulling a few guys towards that genre as many of my SUP mates have jumped ship and don't SUP anymore.
Maybe the travel restrictions from covid aren't allowing as many people to travel to the surf as before.
Finally when summer hits and the xmas holidays come more SUP's will appear on the water I'm sure.
One thing is for sure when I open my shed and decide which one of my 6 SUP's ranging from 7'10, 8'6, 10' to 12ft, I still get pumped and can't wait to hit the surf.