I don't know whether they are just pretending it's ok, so pretending to be ok with settling for their lot or if they genuinely are ok with their lot. I don't imagine they could be comfortable if they are just pretending to be.
I think a lot of it is where we put our priorities/ sense of self worth. So- as an example, I worked a lot of gruelling years in retail. At work, there were people there who detested that job (me included.) But, there were others who didn't appear to mind it and some that were actually happy to be there. It's all the same job but as people, we were different.
The ones who detested it, did so because they wanted to be elsewhere. Mostly, it was the younger people and most of us wanted a career that wasn't retail. If your identity is wrapped up in achieving a career ambition and you see doing a wage slave job as failing that- it's likely going to be upsetting.
The people that didn't mind it so much seemed to either be older: They'd had their careers. They were maybe doing part time hours for a bit of extra cash but that job didn't signify failure to them. Or otherwise, people had priorities in other areas of life- their families, saving up for travel or education. Or, they just didn't seem to have ambitions in life and they seemed fine getting by as best they could.
Of course, overall people still hated it because it's retail and both management and customers treat you like shit but the level of unhappiness seemed to vary according to how we viewed the job I think.
I'm not so sure you can change your priorities in life. I guess you can. You can use logic in a way to do it. Again, I've kind of done it myself. I've realised that my ultimate career aspirations (if I were good enough to achieve them) would see me travelling all over the country and very likely working 16 hour days. That I realised likely would become unpleasant very rapidly! So- that made me more content staying where I am. Plus, I've done jobs that- on paper were a step up for me but in reality- they made me miserable. So, I think you can change your priorities in life but, it needs to make sense to you why you are changing them.
I came to similar conclusions about love and relationships. As in- 'Quit longing for some fantasy of love that very likely only exists in fiction. The real thing is likely nothing like that- or maybe is for just a fraction of the time and the rest of the time, you'll very possibly be regretting it and they very possibly will be too!' Things are much easier to accept when it's in part, your own reasoned choice. But I guess that's the catch- the choice has to feel reasoned out.