Why do I have to pay for a free app

You do not get charged to download a free app. Many of the apps in the store offer in-app purchases, free trial or subscriptions that you would be charged for if you chose one of those options. Developers provide these to allow you to test their app to see if you would like it. They do have to pay each year to have the app in the store for you to download and it does cost them time and money to create and continue to update the apps. Without you having a payment method, there is no chance that they will be able to recoup any of their costs. Apple does not own the apps in the store.

You don’t need to pay for free apps. But you do need a payment method on file, per Apple.