Difference between boost::pfr::tuple_element and std::tuple_element

[denzor200]

https://godbolt.org/z/4odnsoKzK
I know that PFR dont work with const or reference fields. But why don't we remove this restriction in C++17 mode? I suppose that structured binding already has all that we need to do it: https://godbolt.org/z/YbnTevjo5