I would say Amazon’s main business is commerce. They want to be involved everywhere people are buying/selling things. AWS & Amazon.com are coincidences of them starting up around the same time as the internet.

Before long, they’ll own the entire feature for “oh, I need to buy cereal. Alexa buy me cereal. Ok, done. <few mins later>. I’m passing by the Amazon Go store on way home, Alexa. Can I return these shoes I bought last week and pick up my cereal there. Sure.”