If the role requires 3yrs experience it's evidently not targeted at "fresh" graduates, but those looking to move on from their first job.
Graduate roles are more about learning the ropes of corporate life than anything else, and understanding SWE on a larger scale and how to work as a team on big projects with _both_ financial and time constraints.
There is a large administrative overhead with fresh graduates and this is what organisations are unwilling to invest time with - especially if they know the candidate will bounce in a few years.
Most places I've worked which had graduate roles employed people who did their internships with us. They already knew how _we_ did things so the onboarding was very fast.