That's the $64,000 dollar question now, isn't it?
Perhaps they want to maintain the status quo and keep the sheeple in line for as long as possible before the big event.
I honestly don't know why they don't just come out with the truth.
What are they afraid of?
There is a single truth to all of this?
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.
1) The major priority is CONTROL toward the tyrannical gloabal government of super control over citizens.
2) Some, if not all the puppet masters in control of the UFO technologies etc. are terrified that they'll be executed if the public finds out much before the public is effectively totally controlled.