Why UML modeling tools are used in web services?

If we want to create a normal SOAP web service, we write the code in some IDE and output the WSDL file. But when I read the documents, I found that the WSDL file is output from the UML class diagram. Why do you use a class diagram to exit WSDL, and what are the problems? The papers they wrote are listed in the link below. Please explain. https://ieeexplore.ieee.org/abstract/document/1342504/ https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.102.8929&rep=rep1&type=pdf