Why does deque::erase() invoke assignment operator?

Just as the title says, why does deque invoke the assignment operator of the contained type during erase()? I can understand why vector might because elements in a vector are in contiguous memory, but since deque doesn't guarantee contiguous memory, why would it try to move its elements around when some of its elements are removed.

This code fails to compile because my Contained type's assignment operator is deleted and it doesn't have a move constructor.

#include <deque>

class Contained
{
public:
    Contained() = default;
    ~Contained() { }
    Contained(const Contained&) = delete;
    Contained& operator=(const Contained&) = delete;
};

class Container
{
public:
    Container()
    {
        for(int i = 0; i < 5; i++) { m_containerDS.emplace_back(); }
    }

    ~Container() { }

    void clear() 
    { 
        m_containerDS.erase(m_containerDS.begin(), m_containerDS.end()); 
    }

private:
    std::deque<Contained> m_containerDS;
};


int main()
{
    return 0;
}

The MSVC compiler emits this error message:

C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\xutility(2527): error C2280: 'Contained &Contained::operator =(const Contained &)' : attempting to reference a deleted function
1>          ConsoleApplication13.cpp(12) : see declaration of 'Contained::operator ='
1>          C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\xutility(2548) : see reference to function template instantiation '_BidIt2 std::_Move_backward<_BidIt1,_BidIt2>(_BidIt1,_BidIt1,_BidIt2,std::_Nonscalar_ptr_iterator_tag)' being compiled
1>          with
1>          [
1>              _BidIt2=std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>>
1>  ,            _BidIt1=std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>>
1>          ]
1>          C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\deque(1622) : see reference to function template instantiation '_BidIt2 std::_Move_backward<std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>>,std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>>>(_BidIt1,_BidIt1,_BidIt2)' being compiled
1>          with
1>          [
1>              _BidIt2=std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>>
1>  ,            _BidIt1=std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>>
1>          ]
1>          C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\deque(1601) : while compiling class template member function 'std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>> std::deque<Contained,std::allocator<_Ty>>::erase(std::_Deque_const_iterator<std::_Deque_val<std::_Deque_simple_types<_Ty>>>,std::_Deque_const_iterator<std::_Deque_val<std::_Deque_simple_types<_Ty>>>)'
1>          with
1>          [
1>              _Ty=Contained
1>          ]
1>          ConsoleApplication13.cpp(27) : see reference to function template instantiation 'std::_Deque_iterator<std::_Deque_val<std::_Deque_simple_types<Contained>>> std::deque<Contained,std::allocator<_Ty>>::erase(std::_Deque_const_iterator<std::_Deque_val<std::_Deque_simple_types<_Ty>>>,std::_Deque_const_iterator<std::_Deque_val<std::_Deque_simple_types<_Ty>>>)' being compiled
1>          with
1>          [
1>              _Ty=Contained
1>          ]
1>          ConsoleApplication13.cpp(31) : see reference to class template instantiation 'std::deque<Contained,std::allocator<_Ty>>' being compiled
1>          with
1>          [
1>              _Ty=Contained
1>          ]