[dcchambers]

Security and peace-of-mind, as the other commenter requested. Convenience - already having a credit card linked and ready to go.

Also who is to say the developer would charge less? Let's say, for example, a company called ezpay charges $1 per transaction. If an IAP costs $10, they make $7 off the user who buys via Apple, and $9 off the user that buys via ezpay API in the app. They could lower the ezpay price to $8 and still only make $7, but why bother?

[Gigachad]

Virtually no one is concerned with the security of card payments on non apple processors. They have been typing their card numbers in to stripe/paypal/etc for years.

Only the tiniest % of HN idealists will pay 30% extra to have it go through Apple.