Bunkers in the rough exists as an evolution of golf architecture and maintenance...
First, it's hard to mow steep banks so somewhere, on some bunkering style (Oakmont), you can't get the fairway to them.
Second, remember that the word fairway doesn't exist in the rules.
Third, if you design a hole with a bunker in a straight line between the tee and the green and you decide for whatever reasons that the 'fairway' will only be on the left side of the bunker, your bunkers is in the rough.
That lead to one of the most striking element in Forrest Richardson book on bunkers, that bunkers should be an important element of a hole and not only, like most architect do now, put bunker as fill in a fear that their hole will be boring.
That leads to philosophically, bunkers (of the tee) not in a direct line between the tee and the hole could be called pointless.
That's why I have a problem with bunkers on the outside of a dogleg (some call it target bunkers)