Like any comic book publisher, DC Comics puts its best artistic talent on its greatest books. It especially wants good covers, which are effectively the first selling point of a comic as they reel in readers and grab their attention from the shelf. Indeed, many of the most devoted comic book collectors will freely admit to buying their share of comics purely for their enticing covers, whether for the artist or the value.
Source：https://www.cbr.com/dc-comics-series-best-covers-ranked/
