It is not illegal to buy competitors (commenting only on US law). It can potentially violate antitrust laws if you eliminate all competition in a market by buy

It is not illegal to buy competitors (commenting only on US law). It can potentially violate antitrust laws if you eliminate all competition in a market by buying out competitors. But given the existence of Seamless/Grubhub, Uber Eats, and others, plus most of the restaurants still take phone & fax orders, it would be difficult to argue Doordash buying Caviar corners the delivery market.