I could write a book about it -- literally. Maybe someday I will.
Just for starters, you have a problem of authority. In the 1950's, the Church wasn't in crisis, and every priest had a bishop over him, and every bishop had a pope above him, who was not only valid but doing his job and to-be-obeyed.
Today, you have Fr. Cekada, whose only authority over him in this world is Bishop Dolan, who is more of a friend and accomplice than a check on his power. Catholics living at St. Gertrude's have moved there to have access to this mega-parish, and moving elsewhere is not an easy process. Not to mention they've grown quite attached to their 50's Catholic lifestyle.
So, long story short, the potential for BULLYING and TYRANNY is immense. Not just St. Gertrudes, but any other Traditional "mecca".
The Faithful move to these places, making themselves needy and vulnerable (most can't sell their house, uproot, and move away to some other place in the country with anything remotely resembling ease), and in the meantime they form a large group of fat, juicy sheep -- it's natural to attract a hungry wolf or two.
The priests of these places have no earthly authority, so it's easy for them to become tyrants. The priests own the buildings, they run the schools, they provide/control the Sacraments, and the Faithful have little or nothing. Sure, the Faithful might each have a few bucks for the collection plate -- but when you have a parish of 500, who needs a single, particular family? But more importantly, it's easier for them to become corrupt since there is more money and luxury sloshing around. These priests live 10X better than any other missionary/Trad priest in any other part of the country. Both priests and Faithful are WELL taken care of -- daily Mass, parish groups, and multiple priests -- which means the individual priests can kick back a bit, since they're not SOLELY responsible. They get to have "days off" and such.
When a parish grows to a certain size and becomes "well established", the priest can transform from "hand-to-mouth missionary" into a "9 to 5 priest" and it becomes more of a job for him, rather than an 18-hour-a-day labor of love, working tirelessly to establish a chapel on a shoestring budget, and establish a flock from scratch.
The priest no longer needs to be apostolic either, since the large Trad meccas have great word-of-mouth and paid advertising of all kinds, thanks to their immense resources (drawn from a huge congregation). The amenities the mecca has to offer (6 Masses every Sunday, 3 priests living on site, established schools, even colleges, etc.) sell themselves. The priest doesn't need to be a devoted pastor, or anything special. The people will come from all over.
Allow me to explain, with an example from personal experience:
At the Seminary, I remember how much work there was over the summer, when there were only a couple Brothers and 6 or 7 seminarians to do all the work. We had no free time to study, and could barely squeeze in our daily Spiritual Duties. When we had 40 seminarians, the work level was "normal" -- but everyone had a job every week (cleaning floors, bathrooms, setting tables, waiter, dishes, mealtime reader, etc.) and had to work from 1/2 hour to 1 hour every day on chores. However, in my last year the population ballooned to 70 seminarians, so the older seminarians got regular "weeks off" when they had no chores for the week. From a comfort standpoint, it was great. Basically we had economy of scale kick in. Running/cleaning a seminary for 70 isn't much harder than doing it for 40, but you have THIRTY MORE young, adult men to help out.
Compare being a parent watching 10 children -- you have to be on duty at all times -- with being an employee at a company with 20 other employees. Do you have the same level of stress, vigilance, and responsibility? Of course not. You can blend in, you can "get comfortable", you can live high off the hog a bit, enjoy life a bit, coast a bit, slack off a bit, etc. in a way you couldn't if you were the only employee and it was your home business. When there are enough people, YOU CAN BE CARRIED BY OTHERS and if the group is large enough, they won't even notice.
This is why mega-lifeboats (chapels) are so ill-advised today. Not only will the occupants mistake the lifeboat (St. Gertrude's) for the original ship (the Catholic Church), but there is much more potential to exploit the sheep. It's hard for a priest to get "comfortable" when he's flying and driving all around the country, saying Mass for small groups of 20, 50, or 100 people. Such a priest is a missionary like the holy priest Fr. De Smet. He works a labor of love for God and for souls.
Hard work really is good for the soul, and it really does prevent a large swath of sins. This goes for the laity as well as priests.