I grew up in a lower middle class family and I'm wealthier than my parents ever were, just because I worked hard and improved myself, and went into technology where I could make an upper middle class salary.
Why would you want to resign yourself to being poor your whole life?
Not everybody can do that, in fact, most of America can't.
It is very much impossible for most Americans to be coders while maintaining high incomes. The industry isn't anywhere near that big, currently employing less than 1% of the population. Even if it could grow by an order of magnitude, it still wouldn't absorb any meaningful portion of the population.
I think it was a similar situation as the Simpsons being neighbors to the Flanders. As I recall from that show, Ned Flanders actually earned less annual income than Homer Simpson, but had a nicer home and more wealth, because he spent it more prudently.
The implicit assumption in MWC is that no matter how much Al Bundy might earn, Peg and the kids would always spend 101% of it, leaving him with -1% to spend on himself. That makes Al, specifically, the poor guy in a lower-middle household; working all the time with nothing to show for it personally.
Basically they were a rich family like the Cosby show but they loved to LARP that they were poor. A cheap cut-and-paste job where Bill isn't an OB/GYN or whatever he was, but cut and paste him as a retail show salesman without changing anything.
There's a good analogy with how soft sci fi is made, aka the bad stuff. Take a story from another genre and have a computer mechanically cut and paste it into "sci fi" without changing any aspect of the story beyond the crude cut and paste. Superficially shiny and signally, but the slightest attention shows it makes no sense.
From memory the pull the show had was crude language and motivations, in a non comedic manner. It was an appeal to the 80-90 IQ cohort, roughly. Its appeal wasn't the socioeconomic class they lived in, it was appealing to the fart joke demographic, and the producers figured they'd have to bolt on a shoe salesman job instead of OB/GYN because OB/GYNs don't talk like high school dropouts.