They also do that in the developing world except that the things that they stress over are actual matters of life and death.
In the developed world people are stressed because of two things, either they like it or they are creating it themselves by wanting more and more.
Think about it this way. Your typical developing country. I'm not talking about a tropical Nirvana, but i am not talking about North Korea or the Sudan either.
And let's say its rural-agrarian. Thus, this is the normal time-table. They are awake by 5am, they spend the whole day in rather hard labor at their farms, and they are home by 5pm (and normally in bed by 7.30). Stress occurs when rains are late, and thus worries of crop yields arise, or when there is some pest or affliction that threatens their livelihood. Otherwise they are generally not that stressed. They work hard, harder than most people would imagine, but they do not spend their days worrying about feeding their families (remember: I am talking about a typical country ....not North Korea where hunger is a constant, or Sudan where raiders can come anytime). Most stresses in developing countries are to be found in the towns and cities, where things can be quite tough. In the rural areas things can be quite different. And again note,i am talking about typical developing nations. Not North Korea and Rwanda.
And even in those places it has been noticed that people tend to cope with stresses through intense religious beliefs or rather fatalistic tendencies. For example if a Monsoon hits Bangladesh hard the people actually cope with the elevated stress levels pretty well. It hits, they grieve, they move on. Or in Rwanda. A township is attacked, people arte brutalized, women raped. The next day they cry, at times for days, then they pray, and they leave it to God. There is very little internalization. And again, this is in the outlying cases (and just an aside. I am concentrating on typical situations and not these, but even here stress is not chronic. It may be acute beyond comprehension, but not chronic).
In the west the stresses are different (and the vast majority are actually extremely minor .....it is just that people make them into huge things). Again they are to be found in the cities (rural areas have much lower stress levels). And the key thing is not that the stresses are bigger in magnitude, but that they are constant. Most of my workmates are ALWAYS stressed over something. Mortgages, college loans, relationships, credit bills. Some even stress about not getting stressed (they say it feels 'unnatural').
The body can cope with great stress loads ......what it cannot cope with is CONSTANT stress loads. And by the way this is a medical fact.
BTW: When was the last time cortisol medication was offered for sale in your typical rural area (be it in the developing world, or in a farm n Kansas)?