People are sick and tired of cold weather. I'm in the professional recruiting business and these numbers directly reflect what we hear from potential candidates. This trend will continue.
However, I have never believed the notion that warm weather states have better athletes. I think there are just as many good athletes in the North. Just a matter of keeping them in the the North. Refer back to my first sentence.
I don't know if there are as many good athletes in the North. I do still think there are a lot. But less than there once was, due to the population shift. And yes, keeping them in the North is another story.
There was a time when this country largely revolved around the family farms. All throughout the Midwest. This kept those kids close to home. But as family farms have become less and less (more large, corporate entities), families have found less reason to remain North to deal with the harsher winters.