I am fairly simplifying, but you are expected to know your direct dependencies (and normally wil), pagers have embedded escalation rules with prinaries and secondaries, etc. The tooling once you know what to do is better than anything outside of FAANGs I've seen in terms of integration and reliability.

Escalation teams are usually reserved for the "oh fuck" situations, like "I don't work on this site but I found it broken" or "hey I think we are going to lose soon this availability zone" or "I am panicking and have no idea how to manage this incident, please help me".

They're a glue mechanism to prevent silos and paralysis during an event, usually pretty good engineers too.