Everyone (near enough) has some degree of self-interest. If you apply for a job and discover that some other applicant is about as well fitted to it as you and in more need of money, do you withdraw? If you see a $20 note on the ground and no one else around who might have dropped it, do you refrain from picking it up if you think you're better-off than the median person who might walk past next? If you see something you want going for a very good price on eBay, do you contact the seller and say "I think you should be making me pay more for this"?

Unless you are an extremely unusual person, the answers to those questions are somewhere between "no" and "of course not, and why would you even ask?".

If someone is working as a doctor, their work is already benefiting others substantially more than the typical person's. (At least, I think it is; it's certainly doing so more directly.) Being a doctor doesn't put them under some unique obligation never to give any priority to their own interests when, e.g., choosing what job to take where.

If they can save 0.2 lives per day for $50k/year in one place and save 0.19 lives per day for $200k/year in another, it would be virtuous for them to do the former but I can't see that it's obligatory. In the case we're talking about, it might actually be 0.2 lives per day for $50k/year versus 0.21 lives per day for $200k/year, because somewhere that can afford to pay them more can probably also afford better equipment, more ambulances, etc. (In case it isn't obvious, all actual numbers here are made up and nothing I'm saying depends on exactly what they are, only on the rough relationships between them.)

It seems to me like any principle that would oblige them to pick the first of those options over the second would e.g. also oblige all of us who have well paid jobs to give most of what we earn to life-saving charities. Some people do that. It's a virtuous and commendable thing. It would doubtless be better if more people did. But, as you might have noticed, very very few people do that and by and large we don't consider it outrageous that they don't, and I don't see why doctors in particular should be condemned when they don't do it.

(Since clearly unassisted human nature isn't going to make everyone behave in such a way, it seems to me that if we wanted that sort of thing then it would need to be imposed by force. Which in fact everyone might be OK with, in the same sort of way as players of high-level sports are OK with having externally-imposed safety rules so that we don't get everyone playing in increasingly dangerous ways for the sake of a small advantage over people who are being more careful. And, in fact, we do have that sort of thing and it is imposed by force; it's called taxation, and actually I think it's a beautiful thing even though there's plenty to dislike about every actually-existing regime of taxes and benefits. This is mostly a digression, but note that it means that if a doctor chooses to go somewhere where they're paid better it probably also means that they're contributing more to the general welfare in taxes. There are plenty of nits one could pick with this remark, but it still seems worth making.)

Most doctors aren't running departments in major hospitals, or advising government on policy. They don't earn the big bucks. And even hospitals themselves tend to run in the red all the time; it's sometimes hard to disentangle where greed ends, and longer-term interests of patients begin, as you have multiple people and organizations pulling in different directions for different reasons.

RE private medical universities, N=1 but in Poland we have a private provider pushing hard for training their own doctors "because public system is too slow and limited", and it's hard to tell whether they have a point, or whether it's a private-driven attempt at privatizing national healthcare, or a mix of both.