Yes, I think it's a combination of all 3 reasons above, plus a 4th - their fantasy-land idea of how they *think* the Church operated pre-V2, under an actual pope. Some of these dogmatic SV'ers think that in pre-V2 times, an 'imprimatur' on a book meant that it was 100% error free. Or they think that the 'true pope' could never do x, y or z (some minor mistake). Or a 'true pope' could never appoint some lying scoundrel to some official post (as if the pope could read hearts and be an oracle). Or that a 'true church' would approve/deny apparitions within 1 day of hearing of them, and/or respond to every single questionable person, place, idea, book, etc. In other words, a 'true pope' would provide some time of 'orthodox utopia' where there was no error anywhere, no heretics (or if there were, they would be punished immediately), no scandals (or if so, they would be reprimanded immediately), etc.
So they look at a guy like Alois, from the 40s/50s, and since they don't see/can't find any church "approval" (in their minds, the church would approve/disapprove of any and all manner of people like Alois), then we have to ignore Alois. But the foundational error is that the Church has the TIME and MANPOWER to even investigate a guy like Alois. In reality, unless Alois was causing some kind of scandal, it was the job of his bishop to do something. And that didn't happen. Which means that Alois is neither approved or disapproved. But to many people with a fantasy-like outlook on how the 'true church' worked, this is unfathomable.
I think that makes some sense. Unfortunately because many SVs mis-analyze the problem because in reacting to R&R they end up exaggerating the scope of infallibility, where, ironically, despite dogmatizing the 1950s, including things like "Suprema Haec", they stretch infallibility to the extent that NO APPROVED CATHOLIC THEOLOGIAN EVER DID PRIOR TO VATICAN II. I've repeatedly asked them to cite where infallibility "in the strict sense" stretches as far as they claim. They're involved in this back-and-forth with R&R, who go in the opposite extreme where they hold that apart from the once- or twice- per-century solemn definition, nothing else is infallible, and 99% of the Magisterium could turn to garbage outside of those narrow limits. So they counter by exaggerating the scope of infallibility. While they dogmatize pre-V2 theologians (per the phenomenon I've termed "Cekadism"), they ironically exaggerate infallibility to an extent that absolutely NO pre-V2 theologian ever did. Both sides would do well to read Msgr. Fenton's incredibly balanced treatment of infallibility "in the strict sense" vs. infallible safety and the overall indefectibility of the Church.
But, you're not wrong that, in the extreme case, I've actually locked horns with some SVs here who did in fact hold that anything with an
imprimatur on it had to be accepted as being infallible for all intents and purposes, that's how far they ended up stretching it.
MANY mystics went years and years before they got formal approval. In some cases, the Church will intervene to shut them down, since it can be harmful, but in others they just rule the old "non constat de supernalitate", meaning ... there's no evidence that it's supernatural, without necessariliy condemning it. It was not forbidden to consider such things prudently barring some condemnation by the Church. Irlmaier was a practicing Catholic, in touch with priests ... and nobody every shut him down, even if a few criticized him (generally people who didn't know him, and in one case a critic was "converted" after he actually met Irlmaier and conducted an investigation).