And yes, they're not obligated to provide those binary blobs, but since they've been doing it for such a long while, not announcing it well in advance, like they do with the so many services they choose to discontinue, just adds to that list of things I dislike about them.
Yeah, yeah, it's a bit more work to publish those binaries and make sure they work. But they still kind of have to do that, for themselves. So I think it's fair to assume why they did it. Because they made a choice to take a small loss on the devices they would sell for the few GrapheneOS users, and cash in on the walled garden, data mining, ads serving, yada yada, whatever brings the extra money after the initial phone sale.
They know they'll lose some sales, but the few percent of people who'll buy a Pixel anyways but keep the stock OS on it lead to a net plus for them.
They don't care about you liking their hardware and using it like you own it (oh the good old days). They care about you using their software so they can track you better and put ads in your phone experience, because long-term, this is where their money is.