I think it's the styling. Because they are all similar in height, if one of them ends up wearing something that makes their proportions look short, it makes them all look short. Most groups have at least one member that's several inches shorter to solve that.
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LEGS
CHOI YEONJUNS LEGS ARE THE BEST. YOU CANNOT CHANGE MY MIND.
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HE IS SO PERFECT
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HE IS SO PERFECT