How about because that's when kids start deciding which classes to take and which NOT to take. Do you think that maybe, given the negative portrayal of "Geeks" and "Nerds" through out the media, that kids decide that they don't 1) want to work hard, or 2) get the label of Geek/Nerd? Maybe the fact that many teachers are not mathematically inclined/proficient, makes it hard for them to motivate the students, to express a genuine excitement about mathematics (without which all of science and all of nature must remain a closed book), further convincing the kids that math is too hard and not worth it.
How about this for a second reason, straight from the last paragraph
The president convened the panel to advise on how to improve math education. Its members include math and psychology professors [my emphasis] from leading universities, a middle-school math teacher, and the president of the National Council of Teachers of MathematicsPsychology professors? I know, I know, they want to consider "how the kids learn", but come on... math is learned by 1) instruction, 2) examples, and then 3) practice, practice, practice. I don't see this as really fixing the problem. But I suppose everyone will feel bettter.
Oh, and by the way, that this came out today was deliciously ironic. Why? Because today is Pi-day. Yes, that Pi. π. The ratio of the circumference of a circle to its diameter. One of the most fundamental constants in all of mathematics (and the rest of science). But wait. Why is today π-day? Because at 1:59:26 AM the date/time, when written out in order is 3/14 1:59:26.
So happy π-day!