Yes it's not private who you chat with, but the content of the messages are secured and the keys are not stored in a way that's accessible to the central server like most "e2e encrypted" messaging systems. So yes, it's not perfect for journalists and similar people who need to hide the who, but for those of us who just don't want the content of our messages scraped for advertising, anti-minority attacks, or any other reason, it's a convenient, reliable, and well designed system. High availability and ease of migrating my contacts is what's most critical after security for me or my contacts would abandon it. Most can't afford the time, effort, and server costs for high availability of a self-hosted application. And what if that friend who self hosts loses their job or just decides to stop hosting it?

And truly private applications that don't have user IDs make it really difficult to find people when you switch devices so never have really caught on. It's hard to get nontechnical people to put in the effort to prevent having to start from scratch reconnecting with contacts offline to get their online identities every time something breaks. Not to mention if they get popular they will get flooded with tons of spam without a way to limit users to a single identity. It's just very inconvenient and thus for most people not a good tradeoff.