It's like this. Mechanically, RPGs need some sort of attribute/ability that determines how well someone influences others. Some games make Charisma-based skills much more complicated than D&D 5e with lots of social modifiers based on all the things you mentioned. One game I played had Infamy and Famous as Feats. If you were Infamous you would receive penalties for interacting with common folk and nobles and law-abiding citizens. If you were Famous, you'd get bonuses with that same group but penalties with infamous people.

D&D 5e tries to simplify this kind of thing so it isn't so overly complicated. Charisma adds a bonus to certain social skills like Persuade and Deception. It's up to the DM to then apply Advantage or Disadvantage or a +1 or +2 or -1 or -2 based on the circumstances.

As for Charisma bonus based on looks, that's not what I was trying to suggest. Charisma is more than looks. It is about presence and bearing, and it's a natural quality that someone has to be able to somehow naturally influence others.

So, like I said, Darth Vader is as ugly as heck, like an undead, but he has a strong Charisma. His very presence inspires fear and is Intimidating. He also has a great deal of skill in Persuading others, because although he lacks charm, his very presence and reputation make people respect him and do as he says. He is good at Deception as well, because, again, people don't want to question him. His personality and presence frightens them too much to question him.

So, a halfling and half-elf's Charisma bonus has nothing to do with looks. It's about some sort of natural charm or presence or quality that they possess. People just can't help but like them - generally speaking - as opposed to a hag who people naturally can't help but dislike. The hag could be as intelligent and nice as can be, and she could speak well and know exactly what to say, but she would likely get a Charisma penalty by nature simply because of her reputation and looks.

It's about the whole package, not just one aspect of social influence. It's looks, the way you carry yourself, your reputation, etc.