- National Politics (Right doesn't like to acknowledge that obesity and Type II Diabetes is a thing. Which is why when Bush mandated wellness plans for conservatives were upset, so he compromised by making it possible to lose your federal lunch funding if you didn't develop one and execute it - which was supposed to put urban schools at a disadvantage, but actually just ended up hurting poor, rural white schools more. When Obama took office, his wife started the national initiative to support existing urban gardens, but the federal government forbids ANY facility that gets federal funding for food from using garden fresh items on its menu. So all urban farms produce has to be sent home, not served during lunch.)
- Expense (all government functions, including feeding children goes to the lowest bidder, not the best bidder. In most local areas, lunch contracts are very competitive and for many years before wellness plans, awarded to a few companies with political and corporate ties. Now you've got develop a plan that forces vendors to work with you to do the unprecedented, youth focus groups, surveys, tasting days at school, and then implementation. I remember a contractor in a particular city who's only job was marketing the wellness plan awareness competent made around $100K.)
- Learned Behavior (even after wellness plans were enacted, most kids refuse to eat healthy, so districts could say it economically wasteful to introduce too many "healthy" foods. Note, kids and politicians both assume that healthy meant "didn't taste good". )
- Parental Support. (most parents aren't paying attention to what their kids eat and assume they will "bounce back". But they aren't taking into account a number of variables. Less physical education during school hours. a much higher amount of refined sugars, salt, fats, artificial flavors and processed foot products. So in certain communities when parents pushed back or weren't supportive it was all the harder to get plans completed. and once the administration changes, parents are the ones who keep schools to keep their commitments. you can imagine that with Trump in office, there is probably no real enforcement of wellness plans at the moment.
That's just the tip of the iceberg. I could on and on. Basically, most school districts have the bare minimum of a wellness plan and when no one is looking they will serve their children the worst food possible. In some places, schools want poor lunches because they rely on a heavier cut of revenue from the vending machines in their buildings. Like I said, I could go on and on. White schools. Black schools. Middle-class, working class urban, poor rural. The kids are being short-changed.