Peak craft beer implies that the trend is now on a downward trajectory. I don't know if that is the case, craft beer feels really ingrained in the culture at this point.
1. Is there a decrease in craft breweries being started, or total gallons of craft beer being produced?
2. Is there a decrease in beer brewing hobby supplies?
To #2, yes, at least in my area there are about half as many homebrew supply shops as there were ten years ago.
I'm definitely not saying no one is making good new beer anymore, just that the improvements from the ~80s-00s has slowed down.
The uproar is probably more among folks who follow the industry though. Most people have seen Anchor at a grocery store at some point. They were, I'm pretty sure, a natural niche craft brewery before those things were normal. In the same zone as places like Sam Adams or New Belgium or Sierra Nevada. You didn't have to really be "into beer" to know what they were and maybe enjoy buying a Christmas Ale from them every year as a seasonal thing.
To OP's point, there's less places like that now, but that's because I have 3 local breweries I'd be sad about if they closed, instead of 1-2 national breweries. I'd be sad if Trillium or Alchemist closed, but it's not as if I could buy them without traveling to the area, so it's more of a "aww, that's a bummer" and less of a change to my life.
I'm not sure either is better/worse though. We've just moved beyond the sort of craft beer monoculture. We don't just have 2-3 Christmas Ales we all drink, in the same way we don't all watch the Macy's Thanksgiving Day Parade or all talk about the new episode of ER every week.
Weird, it's quite well-known even internationally. I certainly see it regularly in London, at the kind of places which sell imported American beers.
They’re pretty notable, arguably they started the craft beer movement
If you ever looked up the history of beer in the US or US beer styles you would know it. All the people in the craft beer industry certainly do. Maybe the craft beer drinkers in parts of the country don't know it but Steam/California Common is one of the few original US beer styles. And Anchor was one of the first in the modern craft beer revolution.
I have never lived in California.