I think lower income parents are just very low on overall bandwidth in terms of time, energy, and money.
Low quality processed food is quick to prepare and relatively affordable. These people also disproportionately live in "food deserts."
And when you're low on said bandwidth you're not as likely to be able to support your kid through extra curricular activities. Instead, plopping them in front of the TV is a real easy way to get some downtime for yourself.
I just don't think these folks are getting home from their soul crushing low wage jobs and cooking up organic balanced meals from whole ingredients and then taking the kids to soccer practice and ballet by and large. They're fucking spent in more ways than one.