Mozilla and Microsoft certainly think it's important to protect/increase browser share. How old are you? I can remember in the 90s, Microsoft thought controlling the web browser market was so important that they literally gave theirs away for free while their biggest competitor was selling their browser in Target, Walmart, etc. for I forget, like $50?

You control the browser, you control the ad experience, the use data, etc.

It's unclear to me what an App Store has to do with anything. (Microsoft does have an app store, by the way. https://apps.microsoft.com/home?hl=en-US&gl=US )