Back in the Golden Age of comics, the covers generally had nothing to do with the inside. World’s Finest comic showed Superman, Batman and Robin playing baseball, even though they didn’t even appear in a story together in the issue. Captain America and Captain Marvel routinely were shown fighting on the battlefield, whether a scene as such appeared in the comic or not. My own favorite, the Simon & Kirby cover for Adventure Comics #93, was drawn a couple years before the issue was published while they were in the service, with no attempt to link the cover to a story.
Gradually the companies began to use it as a selling point (Captain Triumph in Crack Comics being tailed by the werewolf he faced inside the book) reaching the point at DC were they would come up with a cover using an eye catching idea (“The Amazing Trial of John (Gorilla) Doe”) which the writer would then work up into a story. Marvel went further, with blurbs pushing not only the story (Never Has Anyone fought such merciless foes as…THE ENFORCERS!), but subplots (In this issue…Learn why J. Jonah Jameson really hates Spider-man) and the company. (This is Truly the Marvel age of comics!). We’ve pretty much gone back to the Golden Age, where so often the regular cover has little relation to the comic, and the variant(s) never, all usually being drawn in the hopes of using the art as a poster. Comic regulars know enough to find their favorites, but any newcomer trying to find a book of interest might well be lost looking at the racks.