Network effects are network effects. I really feel physical disgust and try to keep it off my devices, but while it's feasible when living normal, uh, "no-lifer" life, it's unfortunately basically impossible when I travel or even just participate in local communities (sports, hobbies, etc). In the latter case, it's simply rude and disorganizing to refuse to join the group chat, in the former case it's often the only way to contact hotel/taxi/whoever you urgently need to contact in some not so touristy spot. (And, BTW, it's designed to be practically unusable, if you don't allow it to access your contact book, so no dirty tricks like that will fly.)

As to "how do they even manage to use it", well, the mere notion of a great UI is vastly overhyped in the first place (by designers themselves, most of all). People get used to just about anything, if they are taught to use it. And learning a 5-step sequence to use any app like this — anybody can do that, even a 85 year old (even if they swear they can't).