Here's my two cents (the way I've justified this to myself at least)
Let's look at the A minor pentatonic scale, which is symmetric: A C D E G. (intervals 3,2,2,3 semitones.) Now another way building it up from fifths: C G D A E. Indeed either way it looks like D is the central note.
Now let's look at this scale harmonically. We have four fifths, two minor thirds, and one major third, C-E.
With this major third, we can construct a total of two triads: C major C E G and its relative minor, A minor A C E. These are the only fully consonant triads available in this scale.
So the most fundamentally harmonic thing about this set of notes is the pair C-E. Now we normally name an interval by the lower note, as it is the more fundamental. Hence the note that most stands out in this group of notes is the C. So we can reorder to get C D E G A, known as C pentatonic major, or (uniquely out of the five possibilities) simply C pentatonic.
The same applies for the diatonic scale of Am/Cmaj (or simply C). We ad one extra fifth at the beginning and the end and get the following portion of the cycle of fifths: (F) C G D A E (B). Now we have three major thirds, which enables us to build three relative major/relative minor chord pairs: Fmaj/Dm, Cmaj/Am and Gmaj/Em. But again, the most central of these is the major third C-E.