When it comes to retirement for diocesan priests there’s a phrase to remember: “When retirement comes, room and board ends.”
Diocesan priest are “employed” by their assignment. Thus their paycheck and room/food come from their primary assignment. Once retired the diocesan priest does not have an assignment and is essentially on his own for arranging a place to live and food to eat. Even if a priest ends up in a diocesan retirement community he is still paying rent for his room/apartment there.
That’s why some retired diocesan priests stay in rectories. However even that’s not necessarily free. If they’re not paying some kind of rent to the parish then they are at least expected to help cover Masses and hear confessions.