I think an understated reason for Amazon’s continued investments is Alibaba.

Although Alibaba has not made a major push into the US, they continue to invest and learn. 

There are not many companies that could invest beyond “Amazon level” but one of them is definitely Alibaba.

Despite the fact that I don't think they are super-motivated with regards to competition, you always know who to watch in the market.

If we weren't in such a sensitive China political situation, you might even see Alibaba try to acquire some major shipping carriers in the US to push into the market. It's already one of the world's greatest logistics providers.

Another possibility is to acquire a major social platform to kickstart consumer acquisition.

Finally....... Many people talk about eBay but I don't see it. 😀