In West-Europe, yes. Depending on the country or region within, unescapable. Why WhatsApp? That question is easier to answer and understand than one might expect. It was the first of its kind to come to the market at such a hype and level, also while retaining an entry barrier of zero (for the time). So taking in mind that the entry barrier was relative to zero and every donkey and cat could sign up, it hooked also technologically troubling users in politics (local and national). Which in turn spread the name and hype of it even further. As a result, over time, the app became too integrated in society for the average citizen that you simply can't do without any more.
You can't simply escape it, due to it actually having been made properly from a UX point of view for the (below) average user. No entry barrier, for a while a phone number was not even needed as long as you were logged in to android (Facebook hadn't acquired it yet). Every option made sense for the time, integrated backup to GDrive on automic by default. And so on.
The others either didn't exist or were still in deep in development (if not concept). At this time yet. Mind you, they can't force you to join that group!! That is illegal, unless it was required by the contract signed.
Telegram never really caught on, yes it has more users now, but it never really caught on due to its timing. Same goes for Signal, threema, etc... Facebook Messenger probably being the only exception to the bunch. Entry barrier is higher with current timing, since people have become more distrustful to giving their phone numbers, needing to make new contacts, needing at least 2-3 chat apps since everyone is still on the old platform and learning a new UX which is fair for the average user. I did a test once with a bunch of friends and family that can't handle technology beyond the power buttons on their smartphones and in their eyes Telegram and Signal UX doesn't make sense... Why? Because the WhatsApp way of doing things is too heavily integrated into everyday life.
The only other way to know these events, announcements, general information is by email, post, newspaper or word of mouth. And depending on the contents, some of that information is bound by regulation to inform the tenant, for example, by mail and/or other means agreed upon.