Why do the English JoJo's hardcovers have different covers than the original Japanese volumes?

The English hardcovers of Phantom Blood, Battle Tendency and Stardust Crusaders are not the original Japanese edition with a new coat of paint. They are JoJonium, a Japanese deluxe reissue from 2013 to 2015, for which Hirohiko Araki drew brand-new cover illustrations and redesigned the characters in his modern style. The original tankobon covers from the 1980s and 1990s are completely different art.

JoJonium only ever covered Parts 1 to 3 in Japan, 17 volumes in total. So when the English line reached Part 4, there was no new art to license, and the English hardcovers went back to the original tankobon illustrations, set inside a cover design created by VIZ designer Adam Grano.

Part 3 is the special case: it exists in English twice. The 2005 paperback edition wears the original tankobon art, while the later hardcover wears the JoJonium art. Same part, two official English covers, two different artworks.