The thing is that users would rather wait for FB, WhatsApp, Instagram, Threads, etc to get back up than to sign up onto another platform.
Now they run back to more centralized platforms like Twitter, TikTok, etc to complain all about it and vice versa because they never deleted their accounts in the first place.
Let's be realistic, being down for a couple of hours with no oblivious competitor (with the network effect needed) isn't going to hurt whatsapp.