Question

I know that it is possible to have Nullable value types that wraps the value type and gives ability to store null.
But is there a technical reason do not allow the value type to be null or the reason is only conceptual?

Answer 1

A reference type is storeed as a reference (like a pointer) to an object instance.
null means a reference that isn’t pointing to an instance of an object.

Value types are stored as the values themselves, without any references.
Therefore, it doesn’t make sense to have a null value type—the value type by definition contains a value.

Nullable<T> is a value type with a HasValue flag that can be false to indicate that there is no value. It still has a value (when HasValue is false, Value is default(T)), but the HasValue flag tells you to ignore the value.
It has nothing to do with null, except that the CLR automatically unboxes null boxed values to a Nullable<T> with HasValue set to false.