It is shorthand for saying that it is used by engineers working on high-profile, high-impact, software that ships to hundreds of millions of people. Some people might argue that these teams work on some of the most important software in the world. So if the people who work on this important software do a thing, like use sequence diagrams, that is a decently good signal that the thing is useful.

Also used a lot in automotive software development processes for example. Basically, the more safety critical a system is the more formal diagramming / modelling there will be part of the design and development process. It’s important to be able to reason about complexities of such systems across a team / teams.