I bought most of the Before Watchmen comic books that are available until today. While doing some research on them, I found out that each issue comes with different covers, see here for an example of different Minutemen #1 covers.
What is the significance of the different cover arts? Is it from different print runs? Or just to create some diversity?
These is no significance from what I can tell. Alternate covers aim to add diversity, and to create 'rare' covers that can be collected and sold at a premium.
In comic books, a variant cover (sometimes variant edition) refers to an issue of a comic book printed with multiple covers with each unique cover art. Variant covers became common during the "Speculator Boom" of the 1990s, when more collectors became interested in the storage and preservation of their comic books with the goal of future financial gain than reading the comics themselves.
~Variant Covers on wikipedia
