They are afraid of facing something they can't control. Most of all, there would be millions of questions and demands by the people (imagine the election rhetoric. "If I'm elected, I will do everything I can to make the aliens pay the gas tax"),
questions and demands that they would have no answers to at all. Politicians are experts at giving answers and obfuscation.
They couldn't obfuscate their butts out of this one.
True enough!