Historically, Bookbub has been much more likely to pick wide authors than KU authors. Has that changed? If so, then it sounds as if you're right. If not, then I question how BB could be emphasizing Amazon US more if it's still favoring wide authors. The only reason to do that would be if Bookbub had a fairly large number of subscribers interested in other outlets. And if that's true, it seems unlikely that its focus is really changing.
In one of Data Guy's last reports before disappearing behind a paywall, he suggested that indie successes were continuing, but that there was a perception indie success was declining because some authors who had been successful earlier were seeing lesser results. (He didn't speculate on why some were moving down as others were moving up.)
Unfortunately, we don't have enough data to even begin to analyze the situation, but I have to tell you that I've hard complaints (and had some of my own) about poor wide markets since 2012, when I first started.
I did notice more wide sales the first time I went wide, as well as more international sales. My very first month, with no advertising and no clue how to market, I picked up sales in the UK, France, and Germany. Once I was wide, I also started getting sales in places like Apple, BN, and Kobo--about 42% of my total. But that changed the moment I figured out some advertising basics, at which point that dropped to 10%. I went Select for a while, then made one more shot at wide that lasted several months.
Even back then (which was before KU), Amazon was 90%+ of my sales. When I did a general promo, like ENT (several years ago), almost all my sales were on Amazon. When I tried to build a promo around another site, I got no sales. In other words, my experience years ago was similar to yours now. If it were just me, I'd say it might have been because I was a prawn, but I heard exactly the same thing from a lot of wide authors back then.
There have always been variations in how different authors performed in the same markets. And those performances have changed over time, with people reporting greater or lesser success. And I bet there are still authors doing well wide, though we'll see in any chime in.
I know that's not very helpful. I wish I had a comprehensive answer that explained what was happening to you and how to fix it. But we don't have anything like enough data for that.
Oh, one thing you could look at is BookFunnel, where I know you're active. I don't personally get many sales from international markets through their sales promos, though I do get a fair number of international mailing list subscriptions from the newsletter promo, so I know international readers are looking at BookFunnel. Do you see any difference there between how many international sales you used to get and how many you are getting now? That might be one way to test the theory that the shift is something BB and others are causing by policy changes or whether other market forces may be involved.