Those companies are very engineering-led. Boatloads of excellent engineers; deadlines are "it'll be ready when it's ready"; marketing is (and thus marketing deadlines are) light, so there's less planning needed; featuresets are largely defined by the engineering teams.

Anything that is reasonably unpredictable in terms of requirements but needs to be reasonably predictable in terms of feature delivery speed is a good candidate.

We use it because we need to release versions of our software a chunk at a time, and it's the closest we can get to continuous delivery given that constraint.