Why is the "petite but adult" character trope so common and profitable in the anime industry?

I'm a newcomer to anime and I’m curious about a specific design trend. I've noticed many popular characters (like Tatsumaki from One Punch Man) have very small, youthful appearances but are portrayed with a mature or stylized appeal. ​Is this mainly a marketing tactic to sell merchandise to a specific "Otaku" demographic, or are there deeper cultural reasons in Japan for this "youthful aesthetic" in character design? I’d like to understand the business and artistic logic behind why studios choose this style so often. Thanks!