Did they ask the original authors of Radix why it's the way it is?
In 2020, radio buttons weren't easily stylable in all mainstream evergreen browsers. That's usually the case why some components are over engineered. Of course they should have simplified them when all browsers fell in line, but tech debt is hard.
Exactly this. OP fails to understand that there are reasons why it was done this way, and that someone who spent thousand of hours working on this might know something that they don't.