Do you really think WeChat pays Apple for the file transfers for hundreds of millions of copies of WeChat to customer iPhones every month (when you include updates). Essentially at least 100 Megabytes times 100 to 200 million a month.
https://developer.apple.com/library/content/qa/qa1779/_index...
If you don't like it, please, tell Apple (or Google) that bandwidth has to be paid.
Until then, it is irrelevant if the app is 10kb or it is downloaded 12.000.000.000 times.
Please show me where Apple says the $99 I pay every year pays for their Sales, Marketing, Distribution and Operating costs of running the app store and getting me customers.
I guarantee bandwidth has to be paid for. If Apple doesn't write that check the App store ceases to exist.