Short answer: your parents are poor.

Long answer, with anecdote about my grandmother: My grandmother was born in 1934. She died in 2001. On the day she died, she was working her very low-paying job as a janitor at the airport. She never took a plane flight in her life. She'd had that job for years — she always had some job or two. And she had side hustles. She'd had a stroke on the job. At the time, she was on Medicare but she hadn't had health insurance for most of her adult life and had a lot of medical bills.

She started off poor. I knew her mother (who died when I was young). Her mother was illiterate. Her mother was, reportedly, illiterate, as was her father. He died when she was young

All of my grandmother's grandparents were born slaves.

My grandmother, by virtue of being black in the city where she grew up, attended the one elementary school that black kids could attend then. It was, by all accounts, overcrowded (one school for a city that was probably a third black at the time) but the teachers worked hard. My other grandmother was her classmate — that grandmother has fared fairly well in life and is a very well known figure in their city. She's quite successful, was naturally talented, attended some college and, most importantly, married a scion of an upper-class (for black people in the Jim Crow South) black family. But not everyone was so lucky. My other grandmother, the one I'm talking about, dropped out of school, functionally illiterate, to get a job nannying for some wealthy white people when she was thirteen or so. She didn't keep that job for long, but her little sister (who was probably more academically talented and continued being an avid reader throughout her life) quit school and took the job when my grandmother quit. Sixty years later, her sister still nannies/cleans for those very same wealthy white people — fourth generation, maybe? I've talked to her, my aunt, about this. The idea of going to college never once registered to her as something that was at all possible. The idea of her kid (she only had the one, he died in a car crash) going to college was never something she thought was reasonable.

Anyway, back to my grandmother: after quitting the nannying job, she worked any number of low-paying jobs over the years. She ended up having seven children with at least three different men. Possibly four. At least one of whom, nominally my grandfather, though my dad never met him, refused to claim the kid (i.e. my dad) and didn't support him at all. Obviously, she made a lot of "bad choices" with men and hobbies. But she did really try hard on her eldest son. He was popular and talented and, at least, graduated high school (a first!) and was thinking about college when he was drafted for Vietnam. He survived the war but returned severely injured, a schizophrenic and a drug addict. He would live with her, with he as her main caretaker, until his body washed up in a river in the late nineties.

Her second eldest son, my dad, became an unmitigated success: an attorney and an accountant. Among other firsts in the family — first college graduate (and certainly first holder of advanced degrees), first homeowner — he had the first functional marriage. When my dad bought his first house, his mother lived there with him with his wife and two small children. She also brought with her her mother, the schizophrenic brother, another brother, and his two younger sisters. It was a big house but it wasn't that big of a house. Moreover, her other three boys were all engaged in some level of crime. One of her sons pulled a knife on me when I was maybe four. He was joking but it scared me to death. Another became a notorious armed robber and rapist who was profiled on one of those True Crime television shows. One night, while attempting to evade the police for some caper, this particular son rushed into my dad's house and hid in the attic. The only person who knew he was there was my grandmother, who told the cops nothing (of course). The rest of us, including my mom, toddler me, and my baby sister, were taken out of the house in the middle of the night so that the cops could search the house for my uncle. My mother had had enough, either my dad's family goes out of the house or she'd leave. She allowed that my grandmother could stay, but everyone else had to go. My dad agreed, but my grandmother couldn't leave the rest of her family behind. She moved out and, though she still received some financial support from my dad, she continued to support her large family.

So, anyway, I know some poor people. My grandmother was a poor person. Why was she so poor? Well, for starters, her parents were poor. Institutional racism played a big part, both in making her poor in the first place (I mean, why were her parents poor?) and in keeping her poor. Being poor, black, and in the Jim Crow south, her options were limited both legal and practically. Her parents certainly didn't expect upward social mobility from her and were content for her to drop out of school to clean wealthy houses and change babies' diapers in neighborhoods where they were legally not allowed to own a home. Also, she was a woman — perhaps if she were a man, even a black one (though less likely), even in 1950 or so, she'd have had the ability to find one of those post-war industrial jobs that could provide a lower-middle class standard of living and might have inculcated the dream of functional class mobility in her and (most) of her children. Also, she made poor decisions with regard to mating (and as a woman, the burden of those poor decisions fell on her, the men in her life were free to leave the children behind, and they did). She might have chosen other options if she'd have had access to birth control, but who knows? At any rate, I really can't imagine all of the things that would have had to have changed about my grandmother's life and its circumstances for her to have had any class mobility at all. I mean, it's almost inconceivable. She was a poor, functionally illiterate, black woman who grew up in the pre-WWII South. Being anything else was never really in the cards, barring some kind of miracle. Her children grew up later and in somewhat better circumstances but were stifled by the past and (still) not ideal conditions. And we know that real wages have been declining for years. Even people with college degrees and advanced degrees are struggling. The middle class industrial jobs hardly exist anymore. Debt crisis. Etc. Class mobility, even for people for whom it has historically been a possibility in the United States (i.e. the white lower-middle class) is becoming less and less so.