the situation for priests, sisters and brothers in religious orders is somewhat different, and the collection for retired religious you refer to does not assist diocesan priests. Its purpose is to pay for retirement care for retired members of religious orders who have nothing in place to care for them. Recall that it was not until the 70s that the working arrangements for these people changed. In the old days we recall with nostalgia, religious in schools, hospitals etc.worked without pay, hence did not contribute to SS Medicare or pension plans. They could expect subsidized housing, food, clothing and medical care from their orders.
They could expect to retire to their convents or monasteries and receive lifetime care, and do light duties as long as possible.
The structure, organization and status of religious orders changed drastically in the very necessary reforms following V2. Religious became employees of the schools, hospitals or other institutions, with set salaries, same deductions as other employees, health care plan etc. This left the older sisters without protection, and in many orders, due to many factors discussed elsewhere, there were no longer any convents to retire to, and no money to support retirees in any case, since the working members often had to find and pay for their own housing and support like any other worker, and their jobs no longer coincided with communal convent life.
The collection for retired religious goes to help these people who in the natural course of time will become a much smaller group.
Diocesan priests are expected, out of their rather modest salary, to not only pay into SS and Medi, contribute to the diocesan plan, but also prudentially make other retirement arrangments like IRAs, and plan for retirement like any worker. Many priests have been criticized for building their own homes, but they are merely using foresight in having a retirement home ready. Many are also supporting parents or other older family members in need as well. So before you criticize a priest for building a substantial savings fund or building a house, stop and think.
I know of no diocese who has anything formal in place for retired priests, although many make places for them in nursing homes or retirement facilities run by the diocese or by religious orders within the diocese. We have a nursing home, but there is limited space. The retired priests who live there, in fact all retired priests I know of, work to their ability often long hours, as chaplains, supply priests, teachers in diocesan formation programs etc., usually for little or no pay due to SS restrictions.