Because they're rich and spoiled. Mountain Brook, Alabama, is one of the single wealthiest towns in the entire United States.
The MSM is trying to play it down, because they've (rightfully) been excoriated by many for usually only going ga-ga over missing people when they're cute white young females with families that are well-connected in their communities (and can thus easily start the ball rolling on press coverage). And there's no hiding that Natalee is (or was) young, attractive and female. But the MSM can completely cover up the fact that Natalee's family, like those of practically everyone else on that trip, is loaded.
She may just be another "runaway bride" ready to make a book and movie deal. Just call me a cynic.