It's not merely expectations but intergenerational poverty. I get that you think that you came from a less privileged background than your in-laws and in some respects that's true, but even being able to immigrate to the US indicates a degree of social mobility that simply isn't available to the intergenerationally poor in rural America. These are people who grew up in places without anything to do, no training for higher-paid professions available, and who pay first-world expenses simply to exist.

How does one get ahead with 4 children and maybe $2000 of household income per month when rents eat half of that.

This isn't simply a problem of moral failing on the individual level but of failings at the societal level to provide a means for these people to escape poverty.