The answer is: because you can’t.
It’s not designed that way. The design is that an instance of the web service class will be created, and then an instance method will be called.
I can only guess why Microsoft designed it that way. To know for sure, you’d have to ask them. Consider:
- There’s no particular benefit to permitting static methods. Anything you can do with a static method, you can also do with an instance method.
[WebService]class is not meant to be some arbitrary class that happens to be used as a web service. It’s meant to be a class that you created for the purpose of exposing web service operations. As such, there is no need to support classes that already exist and already have static methods.
- The SOAP Header implementation permits your class to contain an instance field of a type deriving from the
SoapHeaderclass. This field will be filled with an incoming SOAP header and/or will contain the SOAP Header to be returned. You could not do this with a static field, as it would be overwritten with each request.
As I said, these are all guesses. The correct answer to the question is, “you can’t because that’s how Microsoft designed it. If you want to know why they designed it that way, you need to ask them”.
FWIW, I just checked, and it does not appear that WCF permits static methods to be operations either.