I’m so stupid. I’ve been overlooking the obvious motivation for Miraak this whole time.
The mantra about “you have forgotten” and “what faithless minds have stolen” plus his line about subduing the chaotic world? The arrogance? It all adds up.
He had 5000ish years to watch the world change, and move on without him. To be forgotten despite his importance in the history of the Dragon Cult and the Dragonborn prophecy. And all that time, he was essentially alone. No one else to focus on but himself. Of course he would become selfish and arrogant. The alternative meant madness. And then he would get angry. Angry that the world just left him behind, abandoned him like Mora did. Him, of all people!
He was going to come back and set that right. The world was going to pay for forgetting him.
So yeah, I’m fucking stupid because that’s obvious and I’m sure everyone else already knew it but I was looking for a much more complicated answer than what’s really there. But it’s still super tragic and sheds a lot of light on things. If the LDB gave him any positive attention… Can you imagine how that would change things for someone conditioned into being obsessed with his own importance to compensate for his actual total unimportance? If someone finally saw how much he mattered?
He’d latch onto that in a heartbeat.