[vector.capacity] p14 says

constexpr void resize(size_type sz);

Preconditions: T is Cpp17MoveInsertable and Cpp17DefaultInsertable into *this.

Cpp17MoveInsertable is defined in [containers.container.alloc.reqmts] p2.3

T is Cpp17MoveInsertable into X means that the following expression is well-formed:

• allocator_traits::construct(m, p, RV)

[containers.container.alloc.reqmts] p2 says

given an lvalue m of type A, a pointer p of type T*, an expression v of type (possibly const) T, and an rvalue rv of type T,

Consider this example:

struct A{
   A() = default;
   A(A const&) = default;
   A(A&&) = delete;
};
int main(){
   std::vector<A> vec{};
   vec.resize(10); // ok
}

However, A is not Cpp17MoveInsertable since allocator_traits<A>::construct(m, p, RV) is ill-formed for A.