Ideally, every MonadPlus instance would also be an Alternative instance and every Alternative instance would be an instance of Monoid. You may find it unfortunate that there are so many operations for the same thing but until the (Applicative/Monad) class hierarchy is refactored, we have to live with it.

Sadly there is at least one MonadPlus/Alternative and Monoid instance that differs:

Maybe

The Monoid instance for Maybe is the lifting of a semigroup into a monoid by adding an identity element, but unfortunately, it does so rather poorly as there is no semigroup class that it can assume for its argument, and so it lifts a monoid into a monoid, while avoiding the use of the underlying definition for mempty. =/

So there is no path forward that doesn't change the meaning of existing programs that makes the Alternative and Monoid instances agree on all Applicatives.

-Edward Kmett