Why can't we use lambdas in constant expressions?

Say we have this:

template<typename T, typename Compare>
constexpr const T& max(const T& first, const T& second, Compare comp)
{
    return comp(first, second) ? first : second;
}

template<typename T>
constexpr const T& max(const T& first, const T& second)
{
    return max(first, second, [](const auto& i, const auto& j) { return i > j; });
}

Simple definition of a max function, right? Compiles all fine, since constexpr is free to choose when to compute at compile time and when not.

But when I do:

static_assert(max(2, 5) == 5, "Boom");

It fails. Clang tells me that the lambda is not valid in a constant expression. And I'm forced to use std::greater<>() instead.

As far as I understand, lambdas are just temporary function objects. Can anyone tell me why they decided not to make them constexpr-friendly? Or is my syntax wrong?