I'll agree that there is a certain (sub-)cultural impetus placed upon tanks to stick around under conditions that other classes would likely leave under because of our position as the, generally, most desired role: we're supposed to be more generous because we're gifted with a special position. It provides an interesting modification to the normal cost/benefit analysis that goes into the decision whether to leave (which is made even if it's entirely subconscious or emotional rather than analytical).
From a perfectly rational viewpoint, all classes would have roughly the same cost/benefit analysis because the opportunity cost is the same for every single role: 30 minutes of DF downtime. Ideally, because of the new duty roulette, variation in base timers could potentially be viewed as relatively constant (or at least minimized) because the bonus for needed adventurers provides people an obvious signal as well as reward to act as an impetus to join, so one would assume that the 30 minutes that a tank loses would be weighed on the same basis as the 30 minutes that a DPS would lose. It doesn't work out like this, however, because people aren't perfectly rational and self interested (economists, humans are not homo economicus; we're homo sapiens; more of you need to realize this), and there are two potential deviations that could describe the thought processes of actual people, though I'm not sure if one is more "correct" than the other or if they both exist in the population but there exists a discrepancy in their commonality in the population (i.e. some people proscribe to the first whereas others proscribe to the second).
From one viewpoint, the tank has a higher opportunity cost because the proportional increase to their wait time is many times greater than the proportional increase to a healer's or DPS's: if a tank can expect to have a wait time that is, at worst, 5 minutes but a healer can expect 15 minutes and a DPS a full 45 minutes, a tank experiences a 600% increase in weight time whereas a healer experiences a 200% increase and a DPS experiences a mere 66% increase. As such, 30 minutes of enforced downtime seems so much worse to a tank than it does to a DPS so they place higher value on the opportunity cost of leaving than the other roles do.
From another, the tank as a much *lower* opportunity cost because their end wait time is still lower and, because the variability is negligible (tanks will very rarely wait more than 5 minutes for a queue pop, even if they're not the needed role, and it's virtually nonexistent a vast majority of the time so the average is maybe 30 seconds), a tank has a reasonably strong estimate of when it will be able to queue up again. DPS and healers, on the other hand, end up with higher end wait times that are also extremely variable such that, even if the averages are the 15 and 45 mentioned before, the variation creates much larger windows, say, 5-20 and 30-60 for healers and DPS,, respectively. Because of the increased variability, which is almost universally viewed in a negative light, and higher end result, which is what people tend to think of instead of the increased comparative cost, the psychological opportunity cost, as opposed to a more rational one, becomes a great deal higher.
Both of these do still ignore the previously mentioned cultural impetuses that are likely attached to given roles, which is something of a difficult sociological question because the value of it depends heavily upon whether people are cognizant or subconsciously aware of the assumed demand and how strongly the pressure to follow it is given your peer group. The fractional and disconnected nature of the subculture of ARR (which is itself a subculture of a subculture of a subculture) thanks to the general isolation derived from separate servers (the only time you interact from people on a different server is through duty finder and whoever you interact with there will likely never interact with you or anyone you ever know again, at least in a sense that their identity impacts the other) as well as the further isolation within the servers themselves from relatively small groups forming relatively iconoclastic socialization groups (i.e. people interact with FCs and LSs to a *vastly* greater extent than their server as a whole, so you that server doesn't even really work as a reasonably definition of the group of people within which you exist, in much the same way that people in New York City are more easily identified, socioculturally, with the borough or neighborhood in which they live and/or work instead of the city as a whole), means that you have a much larger number of groups creating their set of relative values for given in-game behaviors than you would think. The variation, even when you go down to the server level to get a reasonably low estimate number of potential social groups, means that you can never really expect someone to have the same values governing their decision to leave a group that you do even if you *can* expect to see and potentially interact with that person that again.
All of this is probably way more than anyone expected to arise our of this topic, not to mention more than most people even think about, but it's an interesting aspect of the gaming subculture to think about and can potentially allow you to empathize (or at least *understand*) the reasons why someone might leave early or stick it out.
Personally, I tend to be more inclined to kick someone who's being harassing or incompetent (and holding the group back) than leave the group itself: I would rather deal with what I identify as the problem directly rather than screw over two-to-six people just so that I don't have deal with the one that's pissing me off. Even then, if the vote fails, sometimes I will stick around because of my desire to not screw over those 2 people (who apparently *aren't* annoyed by the individual as I am). I almost always leave only when the group is unwilling to get rid of the person that offends me (though, sometimes, if it's readily apparent that the people in the group already know each other or are getting along inordinately well, I'll leave before ever voting because I recognize that the vote would be almost guaranteed to end in that person's favor instead of mine). I'm not sure how common *that* behavioral construct is, but it's the one that I adhere to (and generally recommend that my friends do as well).