Because Gulag pushes them to the top of searches. Idk why retail isn't screaming about this. Search for basically ANYTHING to purchase and the top search results, even on DDG, will show "shopping" for Amazon. Search a specific Adidas shoe, which should show the ADIDAS STORE first, and it'll be Amazon.
Retail is complicit in their downfall otherwise they'd be suing the search engines for unfair competition.