Why do we never use (most) contractions on their own?

Question

“Are you cold?”
“I’m”

“Have you showered?”
“I’ve”

“Is it raining?”
“It’s”

“Am I ugly?”
“You’re”

You get the gist. Why is it so weird to say these instead of “I am, I have, It is, You are”?

In: 614

Answer 1

I’ve read some old timey Enid Blyton book where people respond to proposition with “Let’s”
For example:

“Want to go to the show?”
“Yes, let’s”