公式絵だとちょくちょく貧乳キャラの胸が盛られるのは何故なのか

菜花
https://pbs.twimg.com/media/GbSG_ViakAQnJ66?format=jpg&name=orig
蓮
https://pbs.twimg.com/media/F9rWFo8aQAAzzzJ?format=jpg&name=orig
実唯菜
https://pbs.twimg.com/media/GbSG9V5akAEZSwT?format=jpg&name=orig
https://pbs.twimg.com/media/HLAH1FhaQAEdqRq?format=jpg&name=orig
響季
https://i.imgur.com/TqKpwZJ.jpeg