Amazon, on the other hand, has no such dissonance and has a very profitable advertising arm that could happily benefit from yet more digital real estate. Of all the players out there, Amazon already does massive hosting AND competent ad scheduling across diverse device ecosystems. It just seems like they've got all of the technical side pretty much already up and running; they just need to strap it together in a specific package and ship it.
I know - easier said than done; and who knows what other priorities they're worried about that might not cooperate with owning a "digital town square". For all I know, there's some monopoly law that they'd have to screw with, too.
But all of this is to say: they seem well-positioned, so I'm just idling musing on why they haven't capitalized on it. Your reasoning is as good as any other I've heard. /shrug
So why would Amazon or any other company want to invest in their own version of that?