Premise: The answer has nothing to do with their cause, however, but with the simple fact that dictionaries are not exercises in bi-unique substitutability; in other words, if one of the senses of run is `operate' (as in She runs an engine factory ), that does not make it valid to assume that one can substitute operate for run in We run in the marathon every year .  Although recognizing this as a shortcoming of dictionaries and assigning it arbitrarily to what, for lack of a better term, we might call the  genius  of the language, might seem trivial to the casual observer, it is a valid matter for concern in the realm of lexicology.

Hypothesis: Dictionaries are indeed exercises in bi-unique substitutability.
Relation: contradiction