What specifically changed about Catholic seminaries in the 20th Century?

The Society of Saint Pius X is known to have been founded at least in part because a group of priests/seminarians did not like the changes made to seminaries. >In the midst of the council, everything was changing. In a university seminary, minds react quickly, undergo influences, and seek to understand. We participated at the seminary in all the systematic changes of everything — of the common life, of the house rules, of theology, of scholastics. In the midst of this spiritual and intellectual agitation, we needed to be careful, to reflect, to inquire, and to read a lot in order to remain informed. > >We painstakingly followed such journals as Nouvelles de Chrétienté, Itinéraires, and La Pensée Catholique to follow the conciliar debates. Without these journals, I do not know if I would be a priest today. Without Archbishop Lefebvre, I certainly would not be. The superiors of the French seminary would not have accepted me. My mind was not open to the proposed novelties.[1] The Institute of Christ the King Sovereign Priest was founded under similar circumstances, as its founder had been approached by men looking for traditional seminary formation.[2] And I hear often from conservative and traditional priests how bad seminaries were from the 60s onward. Father Chad Ripperger says in [this](https://youtu.be/gSt_3Z3RVj8?t=1182) video that seminaries became lax in their admissions beginning even in the 40s. What research has been done to show what specific changes occurred in the seminaries and how they came about?