LordArchduke

Just like how we get info about the personal lives of celebrities. Some insiders may leak this info, media picks it up and makes it go viral.

Increase territory and prestige.

They're similar to likes on YouTube. They help increase the reach of any work published on Webnovel. There's a Power Stone ranking for every genre and subgenre as well which helps people discover works endorsed by other readers. Hence by giving Power Stones, you say 'I like this work.'

They're not literally inside the creatures. It's just like drop items from games.

Thanks for the translation and I'll try to find a way to make sure that nobody's feelings get hurt.

lol

Maybe someone is in a place where the mosters are inedible or poisonous hence one may gain power stones but no food but since food is the most basic need, someone may buy it if they're desperate enough. Anyways, there's no loss in putting it as one of the alternate methods to purchase food.

A small spoiler but you really don't need to know martial arts or swordsmanship to fight at later stages when you reach the Saint Tier and above because you use your Domain to fight, which is your strongest weapon.