Why covariance and contravariance do not support value type

Question

IEnumerable is co-variant but it does not support value type, just only reference type. The below simple code is compiled successfully:

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Answer 1

I think everything starts from definiton of LSP (Liskov Substitution Principle), which climes:

if q(x) is a property provable about objects x of type T then q(y) should be true for objects y of type S where S is a subtype of T.

But value types, for example int can not be substitute of object in C#. Prove is very simple:

int myInt = new int();
object obj1 = myInt ;
object obj2 = myInt ;
return ReferenceEquals(obj1, obj2);

This returns false even if we assign the same "reference" to the object.