That's because the data is inherently flawed. The poverty line this year is $15,650 for an individual. That's not poverty, that's destitution. From personal experience, living in WV, you cannot survive on that amount of money without either sleeping under a bridge/in a car or dumpster-diving/shoplifting all of your meals.

Folks say just get on food stamps or medicaid, but it's not that simple. At that level of destitution you may not have a phone, an address, basic ID/documentation, or even a means of getting to the office to apply. Means-testing makes the process so drawn-out and convoluted, that many folks (including myself) don't even bother, because there are more immediate things to worry about (once again speaking from experience).

After years of destitution, I finally managed to make a bit more than twice the FPL and I was still struggling (but significantly better off). Just recently I lost that job for reasons outside my control and after my unemployment runs out I'm back where I started. Everyone I know has a similar story. Any data that says that poverty is decreasing in the US is detached from reality.