Should an adult really be shy, unless they've not had a trauma?

Some people are just shy.. it doesn't matter if they're an adult or what not.

You're mixing up 'quiet' and 'shy'. Shy is a child hiding behind their parent's leg. Not talking at every opportunity is normal behaviour for lots of people. Introversion is a very normal human state which people mistake for shyness.

The idea that everyone has to be a shouty, loud, talkative, non-stop interacting noise box is a peculiar one and makes me think there's a huge lack of social awareness somewhere along the line.

I know the difference between introversion and shyness. sorry, just stating an opinion. i like though how you presume everybody has to be reasoned and wise, instead of being..well human.,

I dislike the word "shy". It implies you're scared of people and the way it's been used over the years it's pretty much an insult now. I got mad when my mum called me shy for not wanting to go on Dragon's Den with my business idea. I basically equate it to being called a chicken. In most cases the correct term is introverted, some people just don't like talking much. I don't see why people like OP must take issue with this, if someone talks a lot is it acceptable to call them out on it?

I don't presume everyone should be reasoned and wise, but the vast majority of people are equipped with the processing power to be aware of those different to them. Obviously different people have different levels of empathy, but almost everyone has some (I assume). Being aware of how different people behave, and why, is a useful life skill.

It isn't a personal attack on you, more a general malaise caused by a society which seems to over-value particular traits, and generates perjorative terms to slap onto very ordinary people.