all for anticompetitive reasons.

Facebook - Buys or tries to buy its competitors before they can become competitors. Examples: bought Instagram (that would have been a huge competitor), tried to buy Snapchat.

Google - Has way too much power in the search engine industry. I don’t remember what its main anticompetitive actions are.

Amazon - due to industry consolidation it has created, it can demand large fees from sellers and sellers don’t have other viable options of places to sell. Amazon also gives search engine optimization to its own products

Apple - anticompetitive behaviors in the Apple App Store