The Internet – The suspicious-looking rocks which some have seen flying across the sky during the past year were not the product of overactive imaginations but actual spaceships, and now these spaceships are on Earth and their inhabitants walk among humans, craving dairy products.
These alien beings evolved on a far-away planet while the streets on Earth were not streets at all but unpaved expanses of land roamed by velociraptors. This planet is similar in size to Earth, with a similar atmosphere, and slightly closer to a slightly cooler sun, so the dominant species on this planet is very similar genetically to humanity. They also went through a long period of history marred by frequent military conflict, but eventually got beyond that point and opted to cooperate with each other and strive toward a better life for all on their planet, a planet which does not include cows or goats or even sheep.
As these extraterrestrial people consumed their plant-based diets and further developed technology, they constructed a microscope which enabled them see for light years as if they were inches. And as they explored the universe from the comfort of their laboratories, they found Earth, and they found out how much the people of Earth enjoy cheese.
Then they quickly built spaceships which let a contingent of lucky young astronauts travel across the galaxy in a span of about twenty years, barely keeping themselves alive by eating nothing but space food. Then they arrived, having mastered English and a rudimentary understanding of American economy along the way, got off-the books jobs, bought some cheese, and enjoyed it more than they expected they would.
Several have already been fired from jobs at cheese shops for abusing the free cheese policy, but this doesn’t appear to have deterred them. The planning committee purposely sent light-skinned astronauts, who have been able to secure high-paying jobs and buy lots and lots of cheese. There may currently be a massive surplus of cheese in America, but more of these cheese-loving aliens are on the way and if they keep eating cheese at this rate there might not be much actual cheese left within fifty years.
Processed supermarket singles are perfectly safe, though. There will always be plenty of those.