I don't know much about the Sumerians. I know any ancient civilization are related to ancient aliens. But it's hard googling about them and not have something paranormal theories come up.
In the simplest explanation, what did the Sumerians believe in, and what is the origin of their beliefs?
Who knows why people who believe in the paranormal believe what they do?
More specifically, Egypt and Sumer are the two oldest civilizations we know and by the 1950s when the UFO craze began, there was little information available to non-scholars about the work being done on the pre-history, so it appeared that both had suddenly appeared on the scene with a sophisticated culture and technology.
Perceived similarities between old world and new world cultures had been written about in works like Ignatius Donnelly's Atlantis: The Antediluvian World and new religious works like Helena Blavatsky's The Secret Doctrine, as well as popular novels like Bulwer-Lytton Vril: The Power of the Coming Race. These works, in turn, influenced pulp sci-fi writers, who influenced Hollywood writers and a man called Richard Sharpe Shaver.
The post-war desire for scientific information, the unscrupulousness of publishers in supplying it and an official stance that led to funding for paranormal researchers just in case they were on to something to give the stuff legitimacy all combined to enshrine weirdery in the American consciousness.
In 1956, The Mole People was released with Sumerian antagonists.
In 1950 Immanuel Velikovsky published Worlds in Collision, which used comparative mythology to promote the idea that mythology recorded a near collision between Earth and Venus.
His work, in turn influenced Zecharia Sitchin who used Sumerian and Babylonian mythology to argue that humans were created as slaves for some aliens.
Finally The Simon Necronomicon made use of Sumerian mythology for its stuff.
The Sumerians are thus fully incorporated into pseudoscience and pseudohistory.