I think in a lot of cases, the person never really had the faith to begin with.
I've seen, especially on FE and SD, quite a few different posters either announce their abandoning of the Catholic religion, entertain it or say they "understand" it, even if they're not "personally there themselves." What has shocked me is that for the most part, such posters aren't met with any serious resistance-- if addressed at all, they're told to stick their head in the sand.
This is actually a fruit of dogmatic R&Rism, as well as Reform of the Reformism. The principles of such theories are so shaky and cannot withstand the indefiniteness of our current situation that without an alternative (you guessed it, sedevacantism!) they abandon the faith altogether.
It's really quite sad. It's ultimately the apostate's own fault, but the insistent R&R clergy contribute to this. Their incessant, brainless and political anti-sedevacantism leaves tormented souls with no other option. They eventually come to despise the Catholic Church and the Successors of the Apostles, because their clergy and polemicists insist on telling them they have to believe their Church is a whore and their hierarchy a conglomeration of fαɢɢօt pimps.
The Orthodox is a nice solution to such a destroyed soul because you retain the ceremonial pomp and circuмstance, but they don't claim any sort of infallibility so if they are taught the wrong thing or their leaders are a bunch of heretics, it really doesn't have any implications like it does in Roman Catholicism.