Because many services eventually become performance bottlenecked either via accumulation of users or accumulation of features. In either case eventually performance becomes very critical.
Sure, but that doesn't make Go unsuitable for those tasks on a fundamental basis. Go is very high performance. Whether Go or another language is the best match very much depends on the problem at hand and the especial requirements. Even in the described case they might have tweaked the GC to fit their bill.
GC pauses aside can Go match the performance of Rust when coded properly? Would sorting an array of structs in Go be in the same ballpark as sorting the same sized array of structures in Rust? I don't know a whole lot about how Go manages the heap under the covers.
