Pidgin was extremely convenient. But it was commoditizing messaging platforms so of course it had to be shot in the head by them.
I don't think anything got "shot in the end"; the protocols of old were often just reverse-engineered too. Few bothered publishing anything about it, which is why Jabber/XMPP was created. Since then encryption made things a lot harder; specifically, E2E encryption. You can't "just" login to a server and send messages, you need to encrypt and decrypt things on the device with the right keys, and how do you handle thin…
That's not 100% accurate. Signal handles message history per device. If you link a new device, you can only see messages that were sent/received after that. There is no way to sync messages between devices, they all get the messages from the signal servers directly.
This also means that you can use signal on linked devices if your phone is offline; you just need the phone for initial sign-on.