Back when competition law used to be enforced, if you used your ~90% market share in one area (such as PC operating systems) to give yourself an unfair advantage in another area (such as web browsers) the government forced you to stop doing that. https://en.wikipedia.org/wiki/United_States_v._Microsoft_Cor....

If the laws were still being enforced, a company that has a very large market share in web browsers, and a very large market share in search, would have to be extremely careful not to "accidentally" break their competitors' products.