A widget, Live Activity, or notification extension is reviewed as its own surface — it needs to genuinely work standalone, follow Apple's interface guidelines for that surface, and can't be used purely as ad space or a way to nag the user back into the app.
Common when a widget is built mainly to show promotional content or an ad rather than the at-a-glance functional info widgets are meant for.
"Your app's widget does not provide relevant, timely information appropriate for the surface, per guideline 2.5.16."