The META-INF/services files:

• java.security.Provider
• javax.security.sasl.SaslClientFactory
• javax.security.sasl.SaslServerFactory

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.