Amazon's "main business" is AWS, not their online store. For many years their store operated at a loss. Don't get me wrong, amazon.com is a HUGE business, but it's not Bezos' breadwinner.
https://www.zdnet.com/article/all-of-amazons-2017-operating-...
AWS is a very large business, and much more profitable than selling physical goods online.
But Amazon's overall revenue was $56.6B (Q3 2018[1]) and "only" $6.68B of that was AWS. By comparison, revenue from Amazon's advertising business is $2.5B - and no one is claiming that is their main line of business.
Even the article you point to shows Amazon made a profit of $1.69B on North American ecommerce vs $1.35B profit from AWS.
So yeah - AWS is a high margin business, but no where near their "main business".
[1] https://www.cnbc.com/2018/10/25/amazon-earnings-q3-2018.html