Sorry, I should've been more clear. You're right - you can absolutely build sequence out of the bind operation for any monad.

Promise.all is not just sequence though, there's some additional subtleties to it. In particular the fail-fast behaviour:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

That's the kind of fundamental coalescing operation that you cannot implement with bind on plain monads.