There are no marriageable young men because lower-class young women prefer exciting thugs to guys in stable, but low-income, jobs. Because welfare allows them to.
If young men saw that getting skilled and getting a job was the only way to have a woman date him, then they would be more likely to strive to get job skills.
When I was young, such jobs were almost exclusively reserved for teenagers getting the first work experience. Adults were never expected to support a household on such wages. Now, it's just about impossible in any urban area. And if all the goof off young males suddenly decided to find such jobs, where would they be? Maybe if you booted out all the Mexicans they'd find work. When I moved to the city where I live now 30 years ago, almost all service jobs were held by blacks and few working class whites. Now most are Hispanic. Plus the influx of immigrants has raised housing costs tremendously.
Of course welfare contributes to the problem, but there's also a biological impulse. If there is no economic framework to support the bourgeois virtues, don't expect any community to learn them. We learn a lot from the discipline and social skills needed to work. But that also requires a carrot as well as a stick.
We have consistently chosen the worst economic, tax, trade, regulatory, and immigration policies beginning with Nixon's going off the gold standard in 1971. Yet even small improvements as we saw with Trump show how quickly the US can recover if those policies are changed.