Developers like in-app payment methods because all they have to do is integrate an SDK for payment, and then they get a monthly payment on their bank account and a bill for accounting, that's it.
If you want to handle payments yourself, you'll have to:
1) implement user management to deal with storing what stuff a user has purchased, with all the GDPR and customer support (forgotten passwords, hacked accounts, lost MFA creds) headache that comes from that
2) find a payment processor that operates in all your target countries (no, Stripe and Paypal alone won't cut it), and integrate these (and hope they don't run into the same issue with Paypal, who are known for deciding on a whim to withhold funds)
3) Issue individual bills to customers, account for stuff like cross-border VAT, insanities like county/city sales taxes, deal with refund laws
4) deal with fraud attempts, angry parents, ...
5) Re-implement recurring payment schemes if your business model wants these
In the end, app stores (and ad SDKs) are a matter of convenience. Big shops like Epic, Spotify, Netflix can get away with running lots of this infrastructure on their own, but 99% of small devs don't have the time, knowledge and legal requirements to deal with that.
Developers like in-app payment methods because all they have to do is integrate an SDK for payment, and then they get a monthly payment on their bank account and a bill for accounting, that's it.
If you want to handle payments yourself, you'll have to:
1) implement user management to deal with storing what stuff a user has purchased, with all the GDPR and customer support (forgotten passwords, hacked accounts, lost MFA creds) headache that comes from that
2) find a payment processor that operates in all your target countries (no, Stripe and Paypal alone won't cut it), and integrate these (and hope they don't run into the same issue with Paypal, who are known for deciding on a whim to withhold funds)
3) Issue individual bills to customers, account for stuff like cross-border VAT, insanities like county/city sales taxes, deal with refund laws
4) deal with fraud attempts, angry parents, ...
5) Re-implement recurring payment schemes if your business model wants these
In the end, app stores (and ad SDKs) are a matter of convenience. Big shops like Epic, Spotify, Netflix can get away with running lots of this infrastructure on their own, but 99% of small devs don't have the time, knowledge and legal requirements to deal with that.