When you open metamask there's a dropdown in the top right. It lets you choose which network you're using, and defaults to "Ethereum Mainnet". If you hit the "Add Network" button you can configure which server your metamask talks to.

How many people switched default search in Google Chrome from Google ? Probably less than 1%, because the overall Google market share is 91%.

Unless there's another equally popular extension, not made by Consensys the presence of that option is irrelevant.

How many more switched it to Google from Bing from Microsoft Edge? Google having 91% market share is an effect, not a cause; they have it because their product is the best and does what I want it to 91% of the time.

If Google’s market share was only a result of a superior product then they wouldn’t feel compelled to pay Apple billions of dollars to be the default search engine on iPhones. Defaults matter.

As other comments mentioned, you can change your endpoint in metamask.

Also, metamask is not the only wallet there is... Some dApps only accept Metamask buts it's becoming rare. Most dApps implement multiple alternatives, like WalletConnect, which is more of a dapp/wallet protocol, which allows you to use any wallet software.