Returning serves is all about ball control. In a rally, the incoming shot is usually more predictable than a serve, which normally has a much wider range of variation – topspin, sidespin, backspin, at all speeds and placements. To return serves, where the incoming ball is far less predictable, it helps to shorten the stroke to maximize control. This cuts down on power, but the shorter backswing gives you more control. (Just as with other strokes, the backswing and follow-through should still be about the same length.) The exception here is against a deep serve where you read the ball well, and so may use a normal loop stroke.
Watch the top players, especially against short serves. Do they rip the ball when receiving? Only occasionally, and when they do it’s because of their extremely high level of play, or because the opponent made an error with their serve (a slightly long or slightly high short serve, or a “surprise” deep serve that doesn’t catch the receiver off guard). Whether they are pushing (short or long) or flipping, it’s all about consistency, control, variation, and deception. And for that, they shorten their swing and gain in all four categories.