Why is the "drinking milk" trope so prevalent in anime? Repeatedly I see that people in animes drink milk, often after bathing. Females tend to say that it helps to grow their chest. Is that true? But also male characters sometimes drink it, like Kurozuma Watarufrom.



Image from thedreamingotaku. Sanae Dekomori from Chuunibyou Demo Koi Ga Shitai in episode 5.

What is the meaning behind the drinking milk trope, what do people gain from it and why is it shown so often in anime?
There's probably no one answer for why they drink milk in general, but as far as the bathing, it's considered a traditional drink in Japanese public bath houses after a soak:


  There is usually a refreshment cooler here where customers can self-serve and pay the attendant. Milk drinks are traditional favorites and sometimes there is ice cream.


Most places don't know how the tradition started but it's been around for a long time and some people say that milk drinks (not just plain milk but also milk+coffee) taste particularly good after a hot bath.