Because, you know, the federal government has abrogated that power for itself ever since the lame duck Congressional session in 2010.
Under the bill, the secretary of agriculture over the next year will draft nutritional standards for all food sold outside the standard meal program, provided it's during school hours and on school grounds. Hot dogs at nighttime football games would be in the clear. But brownies sold outside the cafeteria might not.
Gettman said the federal regulation of programs beyond the official school meals is "excessive." Urging the Agriculture Department to closely consult with local districts as it drafts the new rules, she expressed concern that the salt, sugar and fat contents of the myriad snacks sold to support extracurricular activities could trigger regulatory alarm bells.
This was neither toothless nor pro forma, by the way: local schools (and special ed programs!) are now starting to feel the federal pinch. And not to be impolite about this, but if we're going to play the 'Who is out of touch?' game then possibly the answer is 'A President and First Lady who seem to think that they know better than local school systems about what to feed our kids.' Put another way: Mitt Romney may have teased a woman about her cookie choices, but at least he trusts her enough to let her make them in the first place. I have seen pretty much no evidence that anybody in the current administration trusts any of us at all.
PS: I assume that Congress justified grabbing that particular power under the Commerce Clause: it's the usual wheeze, after all.