I remember 15 years ago working in fast food. Many, many of the employees do exactly this. But it isn't comfortable. I worked with a brother-sister pair from Brazil. They lived together, worked two jobs each 70 hours per week (Dunkin Donuts, McDs, and a hotel between the two of them), lived in a shit apartment with no cable, and still only sent a couple hundred bucks back to Brazil every month. The sister was around 50 years old.
With that money their family was able to afford a house in Brazil.
You sound very presumptuous. I challenge you to find someone you're describing who works in America to support overseas family and ask them how "comfortable" their living situation is.
First of all - you are almost never 'fortunate'. Jobs offers do not fall from the sky usually.
Second - you many live well within your means and then have a car accident, or an ill relative, or something else that will make you into piss poor indebted fella real quick.
The core problem is that a median income lifestyle is a relatively unstable state due to unforeseen circumstances like your example. A poor person stays poor (if whatever happens doesn't kill them) which means that poverty is a stable state. A rich person can weather at least a couple disasters, so that makes it a mostly stable state. If you're in the middle, you are in a more unstable position compared to the extremes.
If everything was just easy we'd all just do it.