I'm wondering why everyone seems to use 2 cadences to build combo points when cadence + power chord costs less energy, casts faster, and gives you more time when you don't have to stand still.

The suggested rotation of 4x(Cadence Cadence Coda), Cadence Coda, Motifs has 1 second of buffer to allow for lag/timing on cadence presses. It costs 710 energy, which after Anthem of Fervor, will be 639 energy. In that time, we'll regen 600 energy, 660 with Motif of Encouragement, so you are gaining 21 energy per rotation with no time to spend it.

Alternatively, you could do 5x(Cadence Powerchord Coda) wait 5 seconds, motif, which costs 700 energy, 630 after Fervor. You gain 30 energy per cycle which can be used for a 6th Coda on 3 out of 11 rotations. You have a lot more buffer time, your Codas always go at 5 CPs instead of 4x 5CP and 1x3CP