The META-INF/services files:
Don't contain all the service provider implementations that elytron dependency is bringing.
From What I understand from elytron provider resolution, the providers are resolved differently for elytron: https://github.com/wildfly-security/wildfly-elytron/blob/1.x/provider/util/src/main/java/org/wildfly/security/provider/util/ProviderFactory.java
So the META-INF/services/* files are not used to resolve the provider implementation.
Nevertheless it is cleaner to aggregate the providers properly in META-INF/services files.