> But it does highlight the poor security of desktop browsers where they are only trusted to do anything when a phone app approves it.

Does it? The browser doesn't do anything, the person sitting at the computer where the browser is running is what performs the actions. The reauthentication and 2fa is meant to authenticate and authorize the user, not the browser.

The attack vector of someone else using your phone using an app that doesn't require (re)authentication is independent of the browser or the app itself being trusted. That your bank doesn't periodically require some kind of re-authentication for their app is a security hole, but because the device could fall into the wrong hands, not because the code/app/browser used to access it isn't trusted.