Why do I have to put in a credit card info on mi Apple ID for verification to get an app?

You will have to have a small amount of money in your Apple ID Account balance, to be theoretically able to buy an app.

Also, your payment method is used to verify the region/country, your Apple ID is registered to.

But you can also use Apple Gift Cards to download content or pay for Apple Services. That way you can remove the credit card information.

What you can buy with your Apple Gift Card or Apple Account balance - Apple Support