I think GP is right that there's plenty of "form, not function" regulation - of the form, "must be no longer than X / no heavier than Y", etc.
But I think GP is wrong in considering this to be a problem. Rules may be expressed in a non-functional way, but that's often just a way to embody functional rules in a heuristic that doesn't require expertise to apply.
For a computing example, you may have a processing algorithm that has a tendency to explode in computational complexity on some datasets, because of complicated algorithmic reasons. Instead of explaining the exact problem to users, most of whom will not be able to understand it, you could determine that the failure mode is very unlikely to happen for smaller datasets, and just say "the input should be no larger than 10MB in size".
Other reason for "form, not function" is coordination - there may be many good ways to do something, but all of them require everyone to do the same thing. So it makes sense to pick a reasonable default and tell everyone to stick to it.