The platform modules should not extend the BOM as that ties the versions of all camunda-* artifacts to the current snapshot. We have certain modules (qa rolling update, instance migration, ...) that use older Camunda versions. With the BOM as an inherited pom, we must declare all dependencies explicitly to use an older version (see for example https://github.com/camunda/camunda-bpm-platform/blob/7.12.0/qa/test-db-rolling-update/rolling-update-util/pom.xml#L23-L47). This is redundant and error-prone.
In addition, this can create a dependency chain such as:
This messes up how the artifacts in the Maven reactor get resolved. I.e. artifact C would not be detected that it will be produced by the current reactor (and therefore must be built before artifact A). Impact: Older snapshots of C may be used in the build and parallel builds may fail (see CAM-11210).