I love it when people try to use this argument as justification when it fails.
Many apps are free. Why is Apple not charging these people to host the files?
Then there are the price differences between apps. Does it cost Apple more to host an app that costs $119.99 (Microsoft 365 Personal) vs an app that costs $69.99 (Adobe Photoshop Elements)? No.
Nah....Apple is just treating their store like a mall does to tenants, only without the rent. Although one could argue that the developer fee is the rent part.