For a several reasons. They may have a job, or jobs, and just don't earn a living wage.
Depending on the economy, there just aren't enough jobs to employ everyone. Yes, the federal government can invent jobs to put people to work. However, depending on where you live, there might not even be enough tasks to invent jobs. Plus, you need Congress to fund jobs programs and one party is frequently hesitant to support that. OR, and this is a big one, the govt. jobs would compete with private sector jobs/union jobs.
Sometimes the available jobs aren't where they live, or they can't reach them.
Not all low-income residents are still employable. They might be seniors, or disabled people. Seniors might be raising their grandchildren, and disabled people have children, or are caring for live-in parents. They can't take on part-time jobs. Disability income is based on a percentage of what they once earned. If you only earned minimum wage and barely-survived when you were fully-employed, living on a percentage of that former income is still not enough. Disability doesn't replace your entire former income. It provides a certain percentage of your former income. Disability, like Social Security retirement income, is capped. Once your reach a certain amount, it is capped no matter how much you earned in your career.
Yes, they might get food stamps, and their kids/grandchildrens are on Medicaid, but that is still not enough to sustain them. Food stamps are severely under-funded in Missouri/Kansas. It's not just that there is not enough funding for the number of people in need of them. It's that the amount of money given to a family is still not enough to prevent hunger, or provide food sufficiency. Most food stamp recipients still have to go food banks. Most food banks don't have enough food for everyone who comes. They run out. Even then, there are many families who still go without meals with food stamps, with food banks, and while working one or two jobs.
So jobs programs, or guaranteed jobs, don't help this population.
Many senior women fall into poverty when their retired spouses die. Especially if the wife never worked outside the home. Say they get $2,500 a month in SS income. That is based on her husband's earning level, and provides for both of them. When he dies, the widow might get $1,500 a month. That might not be enough to sustain her while maintaining their home, her health costs, heat bill, and perhaps raising a grandchild.
I wish many of these problems would be solved simply by paying people a living wage/raising the minimum wage to appropriate levels. That doesn't solve the problem for low-income seniors/disabled though. You would need additional assistance for them.
You'd be surprised how many occupied houses you drive by in KCMO don't have the water turned on, or may have water, but no hot water. Or the furnace is broken, and they heat with space heaters. This is because they can't repair things when they break.
That is why the KC school district provides showers and laundry facilities for their students in some schools. That is why some schools still feed kids breakfast and lunch during summer months when school isn't in session.
We have military families on food stamps.
https://www.rd.com/article/military-fam ... od-stamps/
Minimum income guarantees solve a lot of these problems, and do it in a manner in which people don't have to apply for multiple programs,or states then don't even have to administer multiple programs.