Junk food is tasty and kids want to eat it. It gives you a quick energy boost to stay up to be attentive to their instructor when there tired. It's also cheap so that the less fortunate kids can afford it. It's a big variety so more kids can choose what they want to eat instead of being force to eat food chosen for them. Junk food also brings money to the school.
Junk food is very profitable and that money is much needed. Since so many kids are absent daily and the school loses money. Junk food is very popular it brings in big revenue and it's very easy to obtain. The money the school makes off selling the food can be put to good use. The school desperately needs more books and desks.
When it comes down to it it's the kids choice of what they eat. Kids are going to eat junk food regardless if it sold at school or not so that's not helping the problem. So why not at least make some money that the school needs. The kid should eat whatever makes them happy. Let the parents deal with what their kid eats.
Therefore I think not having junk food in high school is very selfish. The adults behind this rule never had to experience this so they feel its no problem. Also if the school stocks up on food kids don't buy and the school loses money that they already don't have. The kids will still eat the junk food regardless. It's their decision if they want to eat healthy or not so let them choose. Junk food should be sold at school