I think it is because classes in C# are not true objects unlike e.g. in Smalltalk. Instance of Type is just a structure describind the class, not the class itself. (See that you have to use Activator if you want create instance of a Type at runtime).

It will be difficult and confusing to have same semantic for methods of objects and something else. In other words, it is by C# design. It is nothing which would be ordered by OOP paradigm. But from my practice I can see, that this is not important limitation.