You're correct that dominating a single market is bad, but using your dominance of a single market to bankroll taking over other markets is pretty nasty and you

You're correct that dominating a single market is bad, but using your dominance of a single market to bankroll taking over other markets is pretty nasty and you can't trivially do something like that if you aren't already fabulously wealthy from dominating a market. In the case of the article, it's specifically talking about how Google is doing that.