in src/main/java/org/apache/maven/plugins/help/EffectivePomMojo.java [163:167]
private boolean shouldWriteAllEffectivePOMsInReactor() {
Source source = mojoExecution.getSource();
// [MNG-5550] For Maven < 3.2.1, the source is null, instead of LIFECYCLE: only rely on comparisons with CLI
return projects.size() > 1 && (source == Source.CLI || projects.get(0).equals(project));
}