They are/were absolutely not obliged to any maker whatsoever, especially not tires. They choose what they felt were the best/safest tires for the given application.
The Metzeler is not intrinsically a sub-par tire (I'd get 7-8,000 miles per set), they're just not optimal for the everyday rider, especially now with the previously non-existant choices we had not too many years ago. Their cupping issue on the front was a very consistent negative, however their reported lifespan and handling characteristics have a very wide range, dependent upon the user, one's riding style, the road type frequented and road compositions.