The reason I believe that it may collapse is because now when I want to buy something online I rather go to Walmart,Target or to the specific brand store. When I think of Amazon the picture that comes to mind is of shady people trying to scam me out of my money. My perception, even if erroneous, right now is that Walmart is less shady than Amazon when it comes to buying merchandize.
If enough people start to feel this way about Amazon there may come a tipping point and the entire company will collapse. Once the tipping point happens I don't think it will be possible for Bezos to reverse it, though he will spend mountains of cash trying to.
With Amazon the purchasing is seamless. That's where they really win. And they just keep making it easier. Now I can order things with my voice (using Alexa).
Of course, take everything I'm saying with a big grain of sand since this is all anecdotal. I've also purchased from Columbia Sportwear Store and some other brands that I do not remember right now. I guess so far I've been lucky.
Also, doesn't Amazon have unique defenses against this possibility? If sales suddenly fall off a cliff, Amazon has AWS and lots of B2B products that could keep them afloat for a time while they tried to recover. If people en masse decided to stop shopping at Walmart, they would have nothing to fall back on.
All they really need to do is curate their 3rd parties better. Problem solved.
That said, Facebook has a much larger network effect than Uber. The friction to create a profile and attend an driver orientation on a competing ride broker network is much smaller than telling your everyone on your Facebook friends list you're moving to Diaspora.
