I guess there’s no particular reason, except some graphic evolution decided by the various powers that be at Dark Horse. I assume the change of printer is not implied in this, since printers usually follow printing materials that are sent by the publisher.
More relevant, I notice that the « Dark Horse » mention on the spine has been changed to « Dark Horse Books ». Maybe the publisher wanted to put this brand in brighter light, in order to discriminate from the regular floppies or the more expensive artbook or whatever. Changing the brand would have implied to change the design.
Just my thoughts : I may be wrong.