I don't think they are dying, the diehard Weatherby clientele is getting older and more likely to hunt and not post online. The new guy with the Creedmoor, ARC or the PRC is more likely to post online.
You are just seeing the push of technology allowing for the younger generation to be "connected" at all times
You see the shifts all the time if you watch the content, posts or suggested search patterns.
I am guilty of it, I resisted the 6.5 Creedmoor forever, built one and never used it. When I finally did, it earned my respect as an easy to shoot, easy to tune and accurate cartridge. I have 2 now. I broke down and bought a used 6.5 PRC to see what the hype was about, it works. I bought a new rifle with a stiff 22" barrel and McMillan stock and it pushes the same bullets as fast or faster than the 24" or 26" Creedmoor with minimal increase in recoil. I use the 156gr Berger EOL out of both, I have a short 18" 308 using the 168gr Berger Classic Hunter, fast twist 18" 223 and plenty of the 64gr Nosler Bonded Solid Based bullets, 280 Ackley using the 168gr Berger Classic Hunter and I am considering a 7 PRC. Waiting for better brass and more data, I just don't see what it offers me over the 280 Ackley. I also have a couple of safes full of crap that still works in a variety of rifles and chamberings.
I've pissed away a metric ton of money chasing ideas and fads, guess what, I will probably do it some more. My uncle bought and kept exactly 2 rifles, a 257 Weatherby and a 240 Weatherby, killed everything from sheep, moose, bear, elk, antelope and deer in North America and pretty much everything in Mexico and Africa he could afford. I killed my first animal with the 257 Weatherby, made my longest shot on game with the 240 Weatherby and both were topped with Leupold scopes, steel rings and bases. Should be nearly impossible if you believe everything you read.
Because a sample of one, scope, rifle or cartridge doesn't work for one person, or even a couple of people, does not mean it quits working for the majority of users.
I treat YouTube like IG, it's entertainment, I do very little research there. I do use it, but it is just another key, it doesn't weigh heavier in the decision than any other form of research. It also does not take long to figure out who likes to hear themselves talk and I tune out completely.