As I understand it, it's Apples fault for requiring all browsers delivered by it's App Store to be basically wrappers around Safari.

How has Apple not been strung up on antitrust grounds over this?

Because IOS is a small fraction of the smartphone and PC market.

It doesn’t preclude antitrust investigations.

I don't think it is in violation of existing law but I'm totally for addition protections like the ability of users to install software of their choosing on their own hardware including additional app stores.

That's because it's not real firefox. Apple doesn't allow real firefox / chrome / etc and all apps that browse web must use safari's webkit.

Keep that in mind next time you go to buy a phone!