For Amazon, that’s something of a threat: Apple, Google, and Microsoft would be well positioned as OS vendors and there is certainly room to imagine that putting Amazon at a disadvantage similar to what non-default search engines faced (remember A9?), not to mention the value of making it as easy as possible to order things.
What I don’t understand is what all of these people were working on. The hardware isn’t bad but it’s not that kind of investment, and the software doesn’t seem to have improved in years (which seems to be true for the entire field - tons of people using them, mostly for the simple stuff Steve Jobs did in the first Siri demo a decade ago). I’m assuming there were projects which haven’t seen the light of day and quite likely never will, and that there’s probably a great inside story about strategic failures locked up behind NDAs.