Ohhhh Christmas, I knew the theories were somehow gonna be political out of the peanut gallery in ye old comment section. 

When you get a virus your body fights it off... 
When the Earth gets a virus it fights it off... 
Law of Relativity or God works in Mysterious ways, what have you.
Point is...
We got greedy and careless.
Funny thing is we will expunge ourselves eventually. 
Sweetdreams lulz