Legitimate sites without “JobPosting” or “BroadcastEvent” type content would hardly have a good reason to use the Indexing API.
If the penalized sites previously abused the Indexing API, either directly or through an external wrapper, well, that would be a useful signal for Google to flag those sites as spam.
Isn’t the pursuit to fill the content gap a scaled content abuse?
Maybe not, maybe yes…
But if Google says they are trying to reduce unhelpful, unoriginal content on Search and keep it at a very low levels, then chasing to publish the same stuff your competitors have without adding value or information gain is probably a bad idea.