The past two decades have seen the general hypertrophic trend in American English extended to what could be called (for lack of an accepted term) pluriverbation, i. e., the converse of univerbation, the latter being a designation of the process by which two or more words are turned into one. In the case of skill set and data point, two phrases that constantly crop up in contemporary speech and writing, the plural substantives skills and data are both decomposed into the phrases at issue, but in divergent ways. In the first example, where a simple plural skills would have sufficed, the deriving base skill (sg.) is transformed into an unsuffixed adjective. In the second example, the deriving base data, construed as a collective singular (through suppression of the singular form datum), assumes the form of the adjective.
Why? In the case of skill set, beside the impulse toward hypertrophy, one could speculate that the collective meaning conveyed by set imparts a semantic nuance lacking in the simple plural. And in the case of data point, the desire to focus on a specific datum is not well served because of the growing obsolescence of the singular.
But over and above these details, there is overall a strong tendency in American culture toward the engorgement of diction through redundancies, tautologies, and pleonasms of all stripes (as in “advance planning,” etc.). One could easily surmise that some of these hypertrophies arise from a need to be explicit, to repeat for emphasis, but a close analysis reveals that this is not so. Pleonasms, etc. always exhibit a widening of boundaries, and it is undoubtedly true that boundaries are among the most unstable of linguistic entities, more liable to shift (metanalysis) over time than other such units.
A stereoscopic view of the entire variety of cases where an enlargement has occurred reveals what is at bottom a FAILURE OF THOUGHT, of a piece with a “culture of excess.” Linguistic hypertrophy may, in the final analysis, be particularly true of the grammars of historically marginalized groups in society, for whom literacy and education have only recently become as common as among the traditional elites. It would be tempting to speculate that tautological constructions in speech and writing are—in their aspect of characteristically displaced boundaries—a linguistic manifestation of an unstable social identity.