The overall drift in language development is toward greater diagrammaticity (iconicity) between sound and meaning, which thereby necessarily results in the attenuation of the arbitrariness characterizing the fundamental relation of all language structure.
This can be illustrated in the history of English by the gradual gain in scope of the quantifier of mass nouns less at the expense of its counterpart fewer, which according to the traditional norm is reserved for count nouns. Many speakers of American English (but not only) regularly substitute less for fewer where the norm specifies the latter to the exclusion of the former.
The iconic motivation of this usage is twofold. First, less is shorter than fewer, thereby fitting it more adequately than its counterpart to its meaning, namely ‘lesser quantity’. Second, individuation as a semantic category is marked (more restricted in conceptual scope) that non-individuation, so that a drift toward non-individuation is a movement toward the unmarked member of the opposition, instantiating the general iconic (semeiotic) principle according to which language change favors replacement of marked units, categories, and contexts by unmarked ones.