Discord exists because people are killed, stalked, and otherwise harassed from IP exposure. That's its 'be safe' purpose.
It's not simply a chat service. You also have proxied video calls and VoIP. That in itself is far more expensive and resource heavy than decentralized hosters can do at scale.
It's not about proprietary protocols, it's that we already had decentralized solutions that cant protect it's users. Centralization is a requirement at that point if you want it to be popular and scale.
Once again, it's a completely separate issue. You can have a centralized service that also uses an open protocol that people can make custom clients for. Furthermore, people use stuff like Tor for anonymity with decentralized systems. Trusting a central system to keep your information private is a risk of itself.
It's not simply a chat service. You also have proxied video calls and VoIP. That in itself is far more expensive and resource heavy than decentralized hosters can do at scale.
It's not about proprietary protocols, it's that we already had decentralized solutions that cant protect it's users. Centralization is a requirement at that point if you want it to be popular and scale.