Take std::sort and std::ranges::sort as examples, the iterator class in std::ranges::sort is constrained with the concept std::random_access_iterator:

template< std::random_access_iterator I, std::sentinel_for<I> S,
          class Comp = ranges::less, class Proj = std::identity >
requires std::sortable<I, Comp, Proj>
constexpr I
    sort( I first, S last, Comp comp = {}, Proj proj = {} );

But std::sort is not:

template< class RandomIt >
void sort( RandomIt first, RandomIt last );

Why isn’t std::sort (and all non-ranged algorithms) constrained?

A related question: What is the difference between std::fill_n and std::ranges::fill_n?