.NET and Java had good support for statically generating them (correctly even!) from code, but I never had the pleasure of integrating with such a service. Even in that case though, there were developers who used strings for everything instead of the correct types, didn't handle null correctly, etc.
Overwhelmingly in practice people wrote wsdls and xsds by hand, incorrectly, and treated them as secrets instead of publishing them along with the API endpoints. There was other "enterprise" BS during the XML craze too. In one case I even had to work around bugs in an IBM XML firewall, or its configuration. It was a nightmare[1].
[1] https://en.wikipedia.org/wiki/XML_appliance
