But why EJBUserManager.getUsers() is not eliminated? EJBUserManager.getUsers() is a bean (producer method) and it's not an an alternative.
The declaring bean class EJBUserManager is an alternative. But the producer method EJBUserManager.getUsers() is not, is it?

2.6.1. Declaring an alternative
An alternative may be declared by annotating the bean class or producer method or field with the @Alternative annotation.
...
Alternatively, an alternative may be declared by annotating a bean, producer method or producer field with a stereotype
that declares an @Alternative annotation.

There is no @Alternative for EJBUserManager.getUsers(). There is no stereotype with @Alternative either.