Because any binding that isn't on their manufacturer's indemnified list can't be mounted by any shop that sells that manufacturer's bindings, unless they don't give a fuck about liability. Also, the mechanical parts, springs, and antifriction devices wear out eventually. So if you're talking about bindings that are relatively old, no one uses them because no one can be sure that they still perform to the level that they have to, in order to be safe.
Declared the biggest tool on NS.com by StepDad9000
'i'm not too bright sometimes, when i turn my mind off school'
Nolan, after I reminded him of what a verb in the past tense was.
What do I know...I'm Drunk