Today I was prompting my students to think of reasons why the subdominant chord (IV) is more common than the supertonic chord (II) as a predominant within the standard phrase model. As part of this, we talked about what motivates people in the creation of systems and languages. I was aiming at ease of use, pointing out that IV chords are the same quality as tonic chords, and therefore will be easy to play with the same hand shape for most chord-based instruments. But students also brought up the desire for stability brought about by redundancy of information. So the repeated chord quality will emphasize and stabilize the major or minor mode of the tonic more than the II chord. This redundancy is also seen in the tonic note shared between the tonic and subdominant chords.
But all of these stabilizing features also give the IV chord a less effective predominant function. The IV chord shares so much in common with the tonic chord (I) that it can easily move back to the tonic with no real disappointment of unrealized expectation. Thus it doesn't have as strong of a push to move to the dominant chord (V) as the II chord. Thus the choice of predominant is really a choice of motivation. Easiness and stability vs. tension and movement.