My theory, totally without evidence btw, is this. It’s standard coaching practice for kids to be trained early on to improve their weaker foot.
However as they move up the age groups, competition gets so fierce and the jeopardy of not making it becomes real. So they double down on what they’re good at to get ahead.
They practice and practice and practice on improving their crossing, shooting, passing, control on their stronger foot because they simply want to look their best versions. There’s only so many hours in the day after all!
And by the time they break through, they’re back to being one footed again lol