Probably many factors.
-As OP said, no longer making the Bonneville America. Sure, there are still some around but a lot of people who were so active here have moved on to other rides. If a new BA owner finds this forum, there isn't much current discussion to keep them interested.
-Rallies are fewer and farther between. That's how I found this forum before we bought an America LT. I saw a sign pointing to a meeting place for the Noreast rally and followed it to the campground of a group of BA.com members that I rode with few times. The Noreast rally no longer exists. I wanted to ride to the Arkansas rally this year, but the COVID-19 restrictions are keeping me away.
-I am an American and am also turned off by the political discussions on a motorcycle forum. Just don't belong. Don't worry. I won't be flinging bullets. That's the other side of the political divide here in the US.
The dedicated few are making sure that the Arkansas Rally doesn't end up like the rest of the rallies. We're still having it this year, socially distant and masked as required. maybe you'll come next year, we'll be there!