User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-5963861-20130118032003/@comment-124.179.24.74-20130118051759

People tend to either find Brachydios really cool-looking, or the worst looking monster in the series (I'm personally the latter). Those who find Brachydios incredibly ugly might be put off the game if it were on the cover, so Capcom probably decided to change it to a less polarizing monster.