Why is null not allowed for DateTime in C#?

Question

Why it is not allowed to assign null to a DateTime in C#? How has this been implemented? And can this feature be used to make your own classes non-nullable?

Example:

Answer 1

DateTime is a value type, same as an int. Only reference types (like string or MyCustomObject) can be null. Reference types really store "references" to the objects location on the heap.

here's a article I found that explains it better. and here's the MSDN article on it