The communication is in terms of well defined and documented APIs. Which having micro service boundary strongly enforces.
> The system is down - same effect.
Yes if it's a service many other services depends on, but not so much if it's near the leaves of the service dependency tree. In which case the system may still be up with reduced functionality.
If anything, there is MORE communication.
And how many teams who do distributed systems really know what will happen if a critical service goes down? The system is down - same effect.