Those optional dependencies were present in WildFly 26 and below in order to import services from Hibernate Search 5 modules into the Hibernate Search 5 engine, which is needed for Hibernate Search 5 to work correctly: https://github.com/wildfly/wildfly/blob/d018ceb54d3cea3d37d15b55049afdc69f3b3695/ee-feature-pack/common/src/main/resources/modules/system/layers/base/org/hibernate/search/engine/main/module.xml#L47-L60
In WildFly 27, we're relying on the application dependencies to import services, which will then be indirectly exposed to the Hibernate Search engine. An application mistakenly forgetting to import services in the dependency to Hibernate Search modules will not behave correctly. This is unlikely since there's code to automatically add dependencies to Hibernate Search modules (https://github.com/wildfly/wildfly/blob/97c65511edac65ad7e17a208f690dee016ec59c4/jpa/subsystem/src/main/java/org/jboss/as/jpa/processor/HibernateSearchProcessor.java#L116-L124), but still it's possible in some edge cases where this automation wouldn't work.
This is not technically a regression (since the Hibernate Search modules in WildFly 27 are brand new anyway, Hibernate Search 6 being a completely different beast then Hibernate Search 5), but it could damage user experience, so we'd better add these optional dependencies.