Due to the openness of the dWeb, it would be pretty hard to use a centralized payment processor like PayPal, since a developer would have to expose their PayPal API keys within their app's frontend. This would expose their entire PayPal account to attackers and simply wouldn't work. Who wants to support a centralized payment processor anyway? For this reason, dWeb applications are forced to use cryptocurrencies for in-app payments, which is fairly easy to do using smart contracts and authenticators from various blockchains like Ethereum and ARISEN. This also gives developers full programmatic control over their app's earnings and ensures that outsiders cannot interfere in their app's operations.
Learn about exchanging binary data between dWeb peers here.