^ I know, but would you trust your plan of a lifetime, which includes your own resurrection, on the hands of someone like Obito, broke by the death of his crush?
The death of someone close to us can be healed, and thus Madara's plan would go to waste.
Hell even if Madara taught him everything he knew, he still was a 13-14 years old boy which got told off by Yahiko.
I don't know, I don't see someone like Madara, which had the foresight to get the best thing after a defeat ( hashirama's tissue to awaken the Rin'negan ) and transforming it into something massive ( the whole Zetsu tree plus Gedo Mazo ) to give his everything to a kid, swayed by something like that from "I wanna be Hokage! I want to plant trees, create shelter from the homeless and carry old lady's bags" to "I don't care about this worthless world anymore".
Obito's reveal can be debatable as Kishimoto didn't pen a cohesive plot, otherwise, he does make sense. His moon eye plan - in my opinion - is less debatable as even when he was dying Rin was the only thing on his mind. To see his best friend betray him and his dying wish obviously pushed him over the edge.