HR, IT, and facilities each own a piece of onboarding but the handoffs between them are where the time goes.
HR, IT, facilities, and the hiring manager each own a piece of onboarding, but the coordination between them is the part that takes the most time. Making sure the laptop arrives configured, the training plan reaches the new hire on day one, and every system reflects the same start date. Someone is always stitching those pieces together manually, one tab and one email at a time.