It’s taboo to speak poorly about capitalism in the West, and until recently was likewise taboo to speak poorly about the rich. As such, critiques of capitalism and the wealthy have to be concealed, plausibly deniable.
Prior to the 1980s, American alien culture was centered around UFOs, which were often high altitude spy planes being tested by the US government. Interest in UFOs meant interest in greater transparency of the US government toward Americans.
During the 1980s, popularized a decade later, there was a shift in alien culture from UFOs to alien creatures. This matched up with the recognition that the world’s rulers were pursuing an apocalyptic ideology and were no longer caretakers of the earth and living creatures. Aliens became a metaphor for the rulers, who act to destroy the world and it’s people.