It’s not like they binned servo and decided not to use it improve ff. It did improve ff.
They seem to have decided that’s done and finished now. And there’s no longer any need to work on it - whether that’s a wise move or not is obviously up for debate.
Torpedoing the technological future of their browser is bound to reduce that share, at which point Google will likely offer much less money.
They are basically shooting their one trick pony in a leg, deliberately. It’s.... not smart.
In the face of that, it would be reasonable to think that the cost is nowhere near worth the effort, compared to just adopting Chromium.
I think it'd be very easy for them to think that their goals for the modern web are not intrinsically tied to having their own, completely separate software.