I remember Amazon having its own search engine as far back as 2000. So they weren't just a bookstore even then.

That was before AWS came into the picture. Amazon is definitely a tech company that sells widgets on the side, seeing as AWS is where the majority of their profits are derived. By leveraging this large profit margin, they are able to sell at near break-even or even afford to lose some money to attract customers (like prime subscription discounts).

This is how monopolies are started.