The problem is the scheduler doesn't know when a goroutine can do useful work. It thinks that if a new value arrives to a channel there is a good chance the goroutine will do something useful but that's not the case in general. My favorite example is Game of Life (CA) implemented as a network of goroutines communicating their state changes through channels: you have to collect 8 updates from predecessors to update your state, meaning you'll be scheduled to run 8 times before you finally make a real progress. Not good for scalability.