The security angle is easy to understand.
Not sure why Apple cares about control.
But it easier just to want to make Apple seem bad, so there's that.
I would bet Google's track record would easily allow them to defend this in court. More an issue with Google though.
And the problem isn't abstract. Safari lacks a ton of very useful API implementations. Like, try programming a QMK keyboard on an iPhone: it's literally the only platform in the whole world unable to run the Via web app.