...when there's a magic solution that covers them all. Surely such a solution would completely take over the industry, right?

Crickets.

Extremely few successful solutions are built in Xamarin. Their case studies are limited, and are generally close to trivial apps. And when you point this out, Xamarin advocates tell you not to use most of the cross platform stuff, but instead use platform specific code that is layered on abstractions from the underlying tech, always a step behind and a mile too far.

I'm not amplifying anything: The market demonstrates every statement. Xamarin is something that floundering teams buy hoping it gives them a big heads up, and then some time down the path they just end up starting separate projects for each platform.

You obviously are heavily biased, and strangely confrontational, towards Xamarin. But this open sourcing has been met with a universal yawn.