In the recent Kansas interview with +Williamson on the deviations of the SSPX after the death of Lefebvre, he stated his belief that normally "Catholic truth" is welded to "Catholic authority," but since V2, the two have become unhinged, causing some Catholics to pursue authority, and others to side with truth.
He believed that the personal magnetism, charisma, and pre-conciliar eminence and stature of Lefebvre was a 3rd artificial "magnet," which was strong enough to "attract" and hold some.
The excommunication did some damage to the authority aspect of the magnet of Lefebvre (i.e., in the minds of those whose following was predicated upon Lefebvre having retained conciliar authority), and his later death eliminated that magnet altogether, causing his sons and others to look elsewhere ("nature abhors a vaccuum"):
It was back to a choice between truth and authority (the two still remaining unhinged, and there being no 3rd magnet capable of artificially holding both together artificially).
Along these lines, it is an interesting fact that most bishops who convert to tradition only do so after they retire: Thuc, Vigano, Lazo (i.e., authority had a stronger hold on them than truth, otherwise they would have taken their respective positions before retirement).
Others who were consecrated bishops while already in tradition frequently attempt to reconcile with conciliarism (or in fact do): Licinio Rangel, Fellay, de Mallerais, de Galaretta, Thuc (again). For these, whether because of scruple or other reasons, truth started to lose its preeminence, and authority gained the upper hand..
And still others only acccept consecration by the conciliar authorities: Rifan. This is a complete preference for authority at the expense of truth.
To date, only Lefebvre and de Casto Mayer persevered until the end without wavering.
But this battle between maintaining equilibrium between the magnets of Catholic truth and Catholic authority (until they are reunited again in Rome) is where the battle is won or lost; it is where both conversion and defection occur.