Link rot
The steady failure of published links over time, as destinations move, sites close, or the service in the middle shuts down.
It is not hypothetical for short links specifically. Shorteners have closed and taken every link with them, and the people who had printed those links had no recourse, because the domain was never theirs.
The exposure is worst wherever a link becomes permanent: a flyer, a conference badge, a product label, a book. Those cannot be edited, and they will be scanned long after the campaign that made them.
The mitigation is ownership rather than choosing a bigger vendor. A link on a domain you renew survives a change of provider, because the mapping is yours and the name did not move.