There are so many things that we could talk about. I think the simplest thing to realize is that Amazon was losing money for years so that they could become the central hub of vast numbers of shoppers and sellers, and after they got control of the market, they had a huge amount of leverage over all of those people. Now they can increase prices and manipulate search results, as recent court cases have shown us. They also do horrible things to their workers, they try to bust unionization, many of their delivery drivers are peeing in plastic bottles because they don’t have time to stop at a public restrooms, the list goes on and on.
Because it’s such an exhaustive list, and because I don’t think you should take my words at face value, I highly recommend that you read the newspaper. There’s so much great information compiled by people online. When in doubt, start with Cory Doctorow.