Is there any info as to why the cover artwork was changed from the original to this more cartoon-y look? I looked around and couldn't find any discussions.

The one on the bottom is art used on original boxed releases in the U.K. (and possibly elsewhere in Europe? IDK). I've no clue why they used different (and yeah, worse) art from that used in the U.S., but both are technically "original" cover art, just for different regions.