On-chain application will force you to use the service and we need to trust the service, if the service is new and has no reputation, what's the reason I need to risk my money?
You're right, for trusted people and platforms, it can be a waste of time.
But not everyone has a good reputation or verification, and some people don't want to use banks or credit cards.
Crypto with smart contract or script offers many transaction scenarios and methods, and I think it can provide basic trust for almost all deal situations.