I would posit that there is way more supply now, so that makes it harder to stand out in the way a great SSBBW model might 10-20 years ago.
Previously, the barriers were higher to get in, and there were just a few sites with their stables of beauties. They held standards high, so you didn't get models putting out infrequent/crap content. Now anyone with a phone can get their own OnlyFans or Clips4Sale site and post whenever/whatever you want, so you get a lot of amazing women like Hayley (who could make a fortune if she posted better/more frequently) and all too few like Boberry (who has the discipline to milk her looks for all their worth).
The bbw-chan boards are a testament to how great the scene has become, insofar as there are so many models featured here, when back in the Dimensions day, there were relatively few.
Bottom line is the scene has changed and become more defined by quantity than quality, and it most definitely is not fading away.