Miraak was an arrogant fool. His quest for power caused him to turn on the Dragons he once served, gaining favor with Hermaeus Mora and growing in power. And yet he decided to discard even that service. You would think after dying once that he'd learn his lesson about turning against his patrons.
Ararvyne would not make that same mistake. He had plans for the future, and they would be committed under the watchful eye(s) of Hermaeus Mora, Daedric Prince of Knowledge and master of the tides of Fate.