They definitely could. But their rate-limiting schemes cripple any large-size integration. When you have up to a few hundred users, that may work. But if you have thousands of users triggering calls to the Discord API through all the apps that you can connect if Discord even allows it, then you will hit their brick-like rate limits way too fast.

Patreon is much better with that - people can connect all their apps, websites, Vimeo, Discord, Discourse, even desktop software that they distribute, and get them work with their membership at Patreon. There are even GTA servers, GTA mods that distribute member-only benefits to their users via Patreon. I'd even say that its a very good way for desktop software makers to monetize their apps too. Like the PC benchmark software maker OCCT does. (https://www.patreon.com/occt)