Why do people tell girls they are beautiful when they aren't?

because the society its feminazi: if a man dares to call a woman "ugly", he will be called "gay" or "loser"

Unfortunately, the oldest words we have for expressing quality for people are based around beauty and strength. If you know nothing else about a girl, you can compliment her on her beauty. If you know nothing else about a boy, you can compliment him on his strength.

Even if neither is accurate.

Reality is that people search for tools to make other people feel good and these tools work even if they shouldn't.

"I like you" is giving away far more than "You're beautiful".

They are beautiful only when they smile, not many girls are beautiful with straight faces.

Two major reasons for this:-

1) Because they are beautiful in the eye of the beholder. But not to the woman that this man beholds.

2) The man is deceiving the women via flattery in order to obtain some benefit. Usually sex.

It is amazing how an insecure female does not recognise her own beauty. This is not uncommon occurrence.

Who says they aren't? maybe they are but you don't see it (yet)

not hurt feelings

Most of them say that just to get into her pants. Or did you not know that?