Consider the age thing. It is presumed that bishops can no longer function after age 75 as if some sort of physical or mental impairment happens about that time in his life. So, it is presumed in the Roman Catholic Church that such a bishop, upon reaching the age of 75, is compelled to offer his resignation to the pope. It is up to the pope, who in nearly every case is much older than 75, gets to decide then if the guy has the mojo to go on. Or, in more realistic terms, if the pope wants to appoint a new guy who will be more beholden to the theological and social leanings of the appointer. That is the big rub. The pope can go on until he dies or, in the case of Benedict, resigns, but the bishops who administer a much smaller chunk of the pie are past it at age 75.
I am told that there is a little fuzziness in the rubric requiring the offering of the resignation. It may be that he is compelled only to consider it. I do not know the canon law but have read different takes on the rule. In any case, if a bishop were to think about resigning and decide against it, that he had more years of service in him, what would the pope do? I suspect the current pope would call him in and give him a dressing down and even have a prepared resignation letter for him to sign before he leaves. In other words, the bishop has become in Rome a mere figurehead for the pope.
Now if you wish to argue, consider the state of those bishops who have pushed back against Francis. Some of them are facing episcopal reviews of them and their service and may well be forced out. Though in some cases it might be due to incompetence, the majority are reflective of a pope and papal machinery that cannot countenance disagreement -- even one in which the previous position of Rome is what they are holding. Such is certainly the case with the Latin Mass. Again, I have no horse in this race, but it certainly seems odd that not only did the pope decide to restrict the Latin Mass more but took some of the form and privilege of deciding when and where away from the diocesan bishop and reserved it either to himself or those in Rome who do his bidding.
That is not the kind of bishop any Lutheran longs for. It is certainly not the kind of bishop that reflects history. It is once more an evidence of a corporate structure instead of an ecclesiastical one. For what it is worth, in this respect the authority given to District Presidents in Missouri's version of Lutheran jurisdiction is actually closer to the early church than Rome's practice today. Now to be sure, we do not elect those charged with ecclesiastical supervision for life but vote every three years on them and some of our districts choose to have term limits but it would be hard to categorize our DPs as lackies of the Synod President (presiding bishop, if you will). I would never suggest that our system is perfect but only that the evolving system in Rome continues to diminish the bishop in stature and authority in ways that increasingly make him a mere functionary of the pope. The Orthodox ought to have problems with this and so should any thinking Lutheran. This is exactly the reason why Luther found the papal office as it was and as it is to be suspect. It certainly does not encourage anyone to think more highly of bishops and ends up doing the exact opposite.