SvcUtil does not generate code for imported XSDs

[BaerMitUmlaut]

Describe the bug
I'm trying to generate a service from a WSDL that uses requests/responses defined in imported XSDs, and although SvcUtil is reading the XSDs, no code is generated for them and the generated request/response classes are empty.

To Reproduce
Run dotnet-svcutil with a WSDL similar to this one:

<?xml version='1.0' encoding='UTF-8'?>
<definitions
  xmlns:...
  xmlns:xkms="http://www.w3.org/2002/03/xkms#"
  xmlns:tns="some/namespace"
  name="XKMSValidate"
  targetNamespace="some/namespace">
  <types>
    <xsd:schema
      xmlns:...
      xmlns:xkms="http://www.w3.org/2002/03/xkms#"
      xmlns:tns="some/namespace"
      elementFormDefault="qualified"
      targetNamespace="some/namespace">
      <xsd:import namespace="http://www.w3.org/2002/03/xkms#" schemaLocation="http://.../xkms.xsd" />
    </xsd:schema>
  </types>
  <message name="validateResult">
    <part element="xkms:ValidateResult" name="parameters"></part>
  </message>
  <message name="validateRequest">
    <part element="xkms:ValidateRequest" name="parameters"></part>
  </message>
  <portType name="SOAPEntryEUPortType">
    <operation name="validate">
      <input message="tns:validateRequest"></input>
      <output message="tns:validateResult"></output>
    </operation>
  </portType>
  <binding name="SOAPEntryEUServiceBinding" type="tns:SOAPEntryEUPortType">
    <soap12:binding style="document" transport="http://www.w3.org/2003/05/soap/bindings/HTTP/" />
    <operation name="validate">
      <soap12:operation soapAction="" />
      <input><soap12:body use="literal" /></input>
      <output><soap12:body use="literal" /></output>
    </operation>
  </binding>
  <service name="xkms_soap_1_1">...</service>
</definitions>

Please let me know if you need the full WSDL with the XSD files, I may be able to share it privately.

The generated code looks like this:

[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "8.0.0")]
[System.ServiceModel.MessageContractAttribute(WrapperName="ValidateRequest", WrapperNamespace="http://www.w3.org/2002/03/xkms#", IsWrapped=true)]
internal partial class validateRequest
{   
    public validateRequest()
    {
    }
}

Expected behavior
dotnet-svcutil should generate code for the referenced XSD files.

Additional context
Although I was able to use xsd.exe to generate classes for the referenced XSDs, it is missing a significant amount of attributes. I was able to fix it up somewhat but still cannot produce the XML I want. This would also be very hard to maintain.