It may be how you're looking at it. If you do a Forum search on all threads, Air Arms gets a total of 51 pages, Benjamin has 14 pages, Crosman has 53 pages, Daystate gets 64 pages, Hatsan shows 39 pages and FX has a whopping 201 pages. Again, these are pages with threads that mention these names specifically, but if you look in the PCP thread you'll see that the Air Arms Galahad thread has some of the most comments on the first three pages.
In terms of brand recognition, I don't think that Air Arms has the same following in the US as FX or even Daystate. Part of that is that FX has offered more in terms of power and design than Air Arms. While I'm not a bullpup, high tec, or military look fan by any means, a lot of US shooters are and until Air Arms developed the Galahad I don't think the US market looking for those features/styles took notice. Compare this to Daystate offering the Pulsar and the power/shot count of the Wolverine series which is what put them on the US radar.
Shooters in HFT most likely were the ones who knew of Air Arms (that is why I got my Air Arms), but when a custom build is the same as or just slightly more than an Air Arms or something like a Marauder which can be around $500 - 1,000 cheaper, most are going to choose the cheaper to "try" HFT out and if they like it, modify their gun or replace it with a custom or top of the line one. When it comes to air rifles, I think most US shooters will opt for the cheaper gun, but invest a bit more in the optics as that is something they can move to another air rifle or gun if it doesn't work out. When it comes to powder burners, the trend seems to be the opposite.