Why is Apple asking me to pay for free apps?

If any of the six options listed below is true, selecting "None" as a payment method won't appear, and you cannot remove an expired or lost card. In such cases, providing billing information is mandatory.

The "None" option will not appear...

1. If you have an unpaid balance or payment due
2. If you have a subscription that automatically renews
3. If you're using the iTunes Store or App Store for the first time
4. If you are not in the country or region you’re creating an Apple ID for
5. If you changed your country or region
6. If you're a part of Family Sharing

Based on your country of residence and country you have selected under your Apple ID --> Payment methods If you can't download, make purchases, or update apps, including free apps, you must update your payment method or add a new one. If you verified that a payment method is available in your country or region and you're still having trouble, learn more.

In many cases you have to have a valid payment method on file to download apps - even "free" ones.

You won't be charged just to download a "free" app, but many of those are like vending machines or arcade games with "in-app purchases" that cost real money. If you make an "in-app purchase", you will be charged.