Stripe Billing has had this pricing for a few years. For some longtime users of Subscriptions, we originally didn’t change their pricing but are doing so now. We think charging a separate fee for our Billing product is fair, given comparable products in the market (say, Recurly or Chargebee) charge something similar. (Generally more!)
We’ve been investing a ton in making Stripe Billing better. For example, from talking to users we learned people needed it be significantly easier to get up and running with subscriptions. So in the last year we built the Customer Portal[0]. (We’ve also listened to you and improved the analytics[1].) Payments is a low-margin business and our customers are (quite reasonably) very price sensitive. So to be able to make Billing a great product, we realized it was going to have to charge a fee commensurate with the product scope.
[0] https://stripe.com/docs/billing/subscriptions/customer-porta...
[1] https://support.stripe.com/questions/billing-analytics-dashb...