Some of those are going to be subjective calls.
Your three main answers are going to be copyright issues, parallel development and marketing department.
I don't imagine there will be too many copyright issues with covers (might see a name trademark issue -- Resident Evil vs Biohazard) but you will find it for a lot of other things like music, featured characters, in game advertising/rights clearances, likenesses and voice work. Anyway if a dev/pub failed to clear the artist's work for use in North America you might have been forced to make another.
Parallel development. Not so many Japanese-German translators in the US and Canada. Plenty in Europe, also translators and voice actors that speak UK English. To that end you might have had the same game translated twice by both European and US/Canada divisions of companies.
That might have necessitated a different set of boxart if both were happening at different times. One maybe picking the boring and basic CGI where another goes for real art.
Marketing department has a few aspects, I will try not to be too cynical though (I generally think marketing and advertising people are viable candidates to shoot on sight).
What colours do people like? It is generally noted that US peeps like super saturated colours where UK types prefer rather less saturated efforts. Can be as simple as that.
Tastes. Stereotypically US types will be happy enough with the media for kids resembling a John Wick film (though I suppose it is fairly true to life) where most of Europe might question that, however show a female nipple and... I am sure we all remember that superbowl thing where you might see such a thing in an normal hours advert for bodywash in non English speaking Europe at least. Swearing tends to be for Japan if you want the equivalent there. Less of a thing now but post World War 2 Japanese - US relations were interesting compared to Japan-Europe so having some nice kanji on your artwork could be tricky. Ripped from the headlines can also apply depending upon where you are (usually see this more in music, especially if it is anti war or anti politician)
Consumer survey/my gut as an advertising executive says... whether this speaks to people thinking others are, possibly with justification, idiots also comes into play.
Also relevant, he has a few others on similar topics as well
