To be fair, almost all networks that Pidgin could connect to (Jabber/XMPP being a notable exception) used proprietary protocols, and their operators heavily discouraged third-party interoperability.

The difference is that there wasn't any way to do robust hardware attestation at the time (which is what Apple does to frustrate Beeper-like iMessage interoperability), so the reverse engineers usually won.

Here's an interesting story from that time: https://www.nplusonemag.com/issue-19/essays/chat-wars/

The bridges are already free and open source and I don't see my friends and family racing to get them running on their laptops. Pidgin is great, but something needs to be running on a server or you don't get notifications. And without notifications, what's the point of a messaging app?