Distributed, connected collaboration in real-time, at (massive) scale - it's a big functional domain. Offering video, chat, document storage, sharing and collaboration, as well as project management and integration into a plethora of other apps and tools. This is surely a hard space.
Just look at apps that inhabit much, much simpler function spaces - say, Twitter, given the start point of the discussion. It doesn't get that glare of all day, everyday work use. It doesn't have the function and criticality to people's day. Twitter is down? It's just not a thing 99.9% of people will freak out over. Post-pandemic, Teams or Zoom is down means loss of a sales, key workshops stranding participants, distributed Teams losing comms during critical releases, and the list goes on.