Because everyone knows they just wouldn't work in our current world, let alone the laws that would prevent its flight.
But we have laws, passed by the legislature, that mandate the FAA publish new rules specifically covering the integration of this sort of thing into the NAS by 2015. The Obama administration has said, though, that they won't comply with the law, and are taking every opportunity to hinder this sort of thing. There's a reason that outfits like Google are now spending money, hiring, and testing in other countries: because those countries are less hostile to ventures like this.
There's absolutely NO reason in the world why the tests that Google is doing in Oz couldn't be done with farmers just like those in the article, but living instead in rural Iowa or Ohio or California. But no, the administration keeps releasing increasingly bizarre, increasingly punitive, increasingly job-killing "interpretation" of the 2012 law, with spin that runs exactly counter to the plain language and intent of congress. Thank you, Mr. Obama, for chasing ever more innovation and growth out of the country.