Because you want to be insulated from the trouble renters can cause. Heating breaks at 7 in the morning on saturday? Time to call the landlord. They let mold destroy the bathroom? Better have insurance and now hire someone to take care of it etc.
I thought that if I ever get a duplex and rent one side out and live in the other. I would still get a property manager and never let the tenants know I own the place. For context: former landlord.
All of that goes away for a percentage.