you criticize how it is a very "rich 1st world person" way to think about people in the third world suffering because of their poverty by using an argument that sounds 3000% more like a "rich 1st world person", assuming people in the third world or in poorer countries don't know that there is better, or at least different, life out there. The romanticization of poverty is just as much of a problem in the first world as its demonization.
The fact that there are some people who think this way doesn't mean it's the rule, as a matter of fact, your examples just proved it. That old man from the documentary was talking about how the youth went out to look for happiness. It is one man vs a whole youth, a whole group, a whole age group that saw that the world out there was different. Whether they knew about that life's flaws is besides the point, the point is that they know there is a different life, and most of us can't just ignore the fact that it exists or give up on reaching it if it means having it a little bit better. Only one of them ignored it, and not even because he denied life could be better, but because he understood it would be a hard path to trail.
Globalization exists. In the current world more than ever. We know that we're not happy and we know our life isn't the best, even in the poorest of countries, a majority of people still live in cities and have enough access to media - even if outdated - to feel this way. With very few exceptions. As a matter of fact, in poor countries the majority of people are more likely to live in the bigger cities and capitals.
Most of the world isn't farms and tribes without internet, even in most of the averagely poor african country they also have tv and internet to a decent extend, and we want to live in it, we want to live in that tv, in that world that we see through a screen. The logic of knowing no better might've applied 80 years ago or so, but not anymore at all. I live in a third world country in a humanitarian crisis, i watch tv, i speak english, i am here in a kpop forum, i am not the only one either, a majority of my friends are the same. I know how korea is thanks to hallyu, i know how the united states can be thanks to media and internet, even with their flaws, because we are also not all so ignorant that we are blind to the 1st world's problems. But many of us sure hope we could have them instead. Everyone i know does, as a matter of fact, even older people, because they also have or have had at some point in their life access to television, movies, magazines, newspapers and the radio at the very least.
But in return we have to worry about not having (already disgustingly unsanityary) water for a week, which, yes, is necessary to wash dishes, drink, shower, cleanse food, cook, use the toilet, wash our hands in the middle of a damn pandemic, and that isn't exactly simpler or happier. Even when i'm used to it, it's still hard, i still wish it wasn't like that. We shouldn't be "humbly happy" about getting food, because we shouldn't have to worry and struggle every day and every week for food to begin with. We should be thankful? yes, we should be thankful about everything i suppose, but we shouldn't need to be thankful because god gave us a chance to get a full meal for the first time in the month. And even if we had more, we shouldn't become stagnated conformists, ever.
People who live in isolated communities, small towns, don't have access to media or some form of the modern world who think this way are not the rule, by a long shot, they are the exception in a majority of the third world, they are minorities even in their own countries and often they still have had some sort of exposure to the rest of the world that is enough to know that there is different and bigger world out there, as outdated as their view of it might be. With very few exceptions. Even in that documentary you described, you could see that they still knew there was a world out there even if some refused to give in to it. That's how hard it is to find those exceptions.
And all this, not to mention the fact that even if we didn't know better, as
@Yili said, that does not justify it. And even then, even if we know no better, even people who aren't exposed to the outside world know how much of a stress it can be at times to have to struggle constantly for the most basic of things such as water, food and health, trying to at least merely survive to then realize you're not living life, just surviving at all times with no purpose in the long run, knowing that, to most, this cycle is almost inescapable. Many might not have something to compare it to, but many know, at the very least, that they wish life could be easier, better and longer. That they could spend more time with their families, friends, lovers, learning, "humbly" appreciating the world instead of constantly stressing and struggling about what's next in the inhumanly long task of excruciatingly small details we have to run through with the most care to, at the very least, be able to have something edible at the table.