In America this has been the case since at least the 90s. School lunch budgets/prices did not keep up with inflation since the 70s, and increases in the costs of lunch cook labor means the same money does not provide like it used to. Schools have nearly universally converted to reheating the cheapest frozen foodstuffs from whichever supplier provided the best kickback to the board.
Meanwhile kids themselves have participated in the problem. It's common to have several different choices for lunch, with a daily rotating menu "hot" item/meal, or choices of cheap staples like chicken burgers, peanut butter and jelly sandwiches, and the worst quality "pizza" you can imagine, think if Domino's found a way to cut their supply costs in half. A shocking amount of children will insist on eating that god awful pizza every single day. I couldn't understand it when I was a kid, and I was super picky at the time!
Michelle Obama wanted to improve this, but she was called a communist and a man and a monkey, and now conservatives all belief this poor quality school lunch problem is her fault? It doesn't actually make any sense.
We had a 2 tier system in cali. The poor people ate state provided slop and the slightly less poor people ate fast food. We had Pizza Hut, chick fillet, chipotle. Both were unhealthy options tough and option 2 was quite expensive even back 20 years ago it was 10$ or so.