I've been watching this corporate stupidity train wreck play out over the last few months. Every time I open whatsapp I get an obnoxious dialog urging me to pretty please accept their T&Cs. I click it away because I can. The fact that I can amuses me because it signals a certain amount of despair by Facebook. It's not normal for an app to be usable without accepting the terms and conditions.
The dilemma Facebook has is the very real problem that people are opting to uninstall rather than accept. Their users are angry and disgruntled. Which is why they are allowing people to use the app without accepting the terms and conditions. Which is of course highly unusual. From a legal point of view, until I agree, the old T&Cs apply. Basically they are saying those were actually fine and nothing really changed and it's all cosmetics but bla bla bla could you please accept the new ones anyway. It's a very weird position to take legally.
Either the old T&Cs were fine and there never was a reason to change them or the new ones materially change the old T&Cs and they should just state in plain language why and how. Instead we get this months long weaseling that is no doubt partially inspired by the fact that they are under a lot of scrutiny by authorities in the EU and US for privacy violations, monopolistic tendencies, data leaks, etc. The real issue is that the new T&Cs are of course designed to carve out some legal wiggle room there for Facebook to do user hostile things like ads and tracking. So they are in fact a change and they need users to swallow that.