I'm sorry to hear what has happened and it must be just a huge shock for you that your parents are splitting and that he's left her for another woman.
I think to one degree or other in all countries and cultures of the world, men or at least many men feel "entitled" to "buy" women for relationships/companionship/sexual services/domestic services (sometimes all of these.) Think of the older, wealthy men in the UK who have younger, conventionally more attractive partners. I'm not saying there is anything wrong with having a life partner who is older, younger or in any other way quite different from you. What I'm saying is that there tends to be more of a pattern of this even in this country where the man is older, more powerful, more wealthy and the woman is younger, less powerful and with fewer resources of her own.
In other settings, where there can be an even more vast socio-economic gap between people - like that between expat Europeans and resident people (say China,) it perhaps creates even MORE opportunity for MORE men to be in that privileged position of being able to "buy" women. By "buy" I don't mean money necessarily changes hands (although sometimes it does,) but more a woman with less wealth, influence or future prospects is able to gain more financial security, status and potential prospects in a relationship with a man who who has these things.
I do think that there may be specific issues for expats living in other countries and cultures not just because of often having greater socio-economic privilege than those resident. Often, the social, political and cultural values may be different than from where they come from. Often these afford even greater privileges to men than they do in say the UK. Some expat men relish this and take full advantage of what is suddenly on offer. They can also convince themselves that what their doing isn't such a big transgression because they are doing it there rather than back in the UK. I've heard this argument, for example, from men who buy sex and/or have relationships with underage girls or boys.
It's my understanding that also in relatively small expat communities, where people tend to "know" each other, they can sort of "egg each other on," if that makes sense. You said everyone else in your father's firm left their wives for younger local women. That then creates a sort of "culture" amongst expat males where that is considered an okay thing to do.
Perhaps it's just an extension of a sense of male entitlement coupled with greater opportunity to act on that and less of a sense that it's wrong.
Again, really sorry to hear about your experience.