Since Windi CSS is MIT, and Tailwind JIT doesn't seems to have copy or took any of the code from Windi CSS. What is the problem here? Copying an idea?

There's just a tremendous amount of craftsmanship in between a great idea and a great product. And as you evolve that great idea, it changes and grows. It never comes out like it starts because you learn a lot more as you get into the subtleties of it.