When? Source?

In 2016, Apple reduced subscriptions to 15%.

https://www.businessinsider.com.au/apple-changes-app-store-r...

And nearly every app pivoted from a buy it once model to a pay monthly/annually model. Absolutely made the state of iOS apps worse for end-users :-(

It pivoted because there isn’t a way to do upgrade pricing.

That's not a reduced margin on IAP, that's a different serrice with a different model, and 15% is only after a (quite high) threshold.

Very few mobiles games can be sold using the subscription model.