Why i need to pay application that i already uninstall when i want to install that apps again ?

Generally, you don't.

Apple keeps track of which applications have been purchased by any given AppleID account.

You're free to re-install an app if you've deleted it.

The counter to this is if the application developer has discontinued the app or has a new (paid) upgrade option.

The screen you're seeing looks more like the account verification screen (to verify who you are, and that you're entitled to install the app) more than any actual charge.

Who says you have to pay?

The Message is just asking you to verify your payment method. If there's an issue with it, you will need to resolve it before you can download apps, update apps, or re-download apps you have already purchased. It will not charge you again for it if you already own it.