I suspect that there's an interplay of concerns, one being that of the discomfort with not being part of a larger organization, including practical concerns about who's going to provide for their material needs, or health issues (as many of the "old guard" are getting up there in years), which then feeds into this notion of not being a vagans priest, the former leading to rationalization in terms of the latter. In essence, it would take a "red light" scenario for them to leave. As long as they consider it to be a "yellow light" situation, they feel they can do more good for souls where they're at, not have to worry about their material needs, etc. Until it gets to the point of creating a crisis for their own conscience, they don't feel enough of an incentive to leave. So, for instance, a priest who harbored doubts about NO orders might be pushed to the brink by being stationed in the same priory as an NO priest who had not been conditionally ordained. But short of something like that, they just don't see the urgency of parting ways with SSPX.
So this would explain why they haven't actually broken with SSPX. What I'm more focused on here is that they do think differently about the Crisis than the younger generations, and for that reason they're kept out of positions from which they might exert any influence (priors, seminary professors, superiors, etc.), whereas ordinarily these more experienced priests are the ones you would WANT to have influencing and guiding the younger ones.