>>47063162The more detailed the backgrounds get, the more retarded turn-based combat looks. By keeping the backgrounds minimalistic, the player is reminded that it's just an abstraction and prevented from asking questions like “Why are they just standing there? Why isn’t something happening in the background? Why can’t we move around?”
From Gen 6 onwards though, the battle backgrounds actually match up with the overworld. Before, you were essentially transported into a pocket dimension when you battled, but now, these questions become impossible not to ask, because your Pokemon are literally fighting on the same route/cave/town that you're in.