Just about any composer worth his/her salt (and quite a few who are not) have written Mass acclamations -- the Sanctus, Mystery of Faith and the Great Amen. Some of these are noble and singable. Examples are Marty Haugen's Mass of Creation and David Haas's Mass of Light, version that are pretty common up here in the Northeast. As a member of the assembly, I almost never tire of singing the same acclamation every Sunday. Like the intro music to a favorite news station or TV show, their very familiarity is comforting.
So why do choir leaders change them so often?
There are some legit liturgical reasons. Some acclamations may be more suited to a particular season. Richard Proulx, for instance, wrote acclamations based on "O Come, O Come, Emmanuel" -- clearly appropriate only at Christmas.
But are there bad reasons for changing acclamations? Sure.
One silly (if honest) choir leader once told me that the acclamations are changed so the choir would not get bored. Yikes! As liturgical ministers, should not the choir ask whether the assembly is bored? In this particular parish, just as soon as the assembly caught on to a new set of acclamations, they were changed again. The assembly was in a constant state of flux, and spent more time focusing on the changing acclamations than on the Mass.
Another classic sin is to allow home-grown acclamations. Now, unless you are a Haas or a Haugen or a Proulx or a Joncas or a Hurd (and sometimes even then!) you should never sing your own acclamations. Why? First of all, because they are probably nowhere as good as you think they are. And second, what about the visitors and the occasional Mass-goers? Shouldn't they get to sing-pray too?
In my ideal world, the basic acclamations would change yearly, with easy-to-learn versions maybe thrown in for Advent, Lent or Easter.