They didn't understand, how could they?
Bran didn't do it out of greed or hatred. He did it because it was his duty and fate to sit on the Iron Throne.
It was his destiny, but to fulfill it, he needed to use all the players involved in the game of thrones as his own personal pawns.
Just as he broke poor Hodor's brain all those years back, he did the same to Daenerys. Only she could still speak like a normal human being.
Her heart, though, her mind, was corrupted by Bran's hand.
He made sure paranoid thoughts hounded the Targaryen heir, and he poisoned his sister Sansa against the dragon queen as well.
Worse of all, sensing Jon's love for Dani, he was forced to ruin those noble feelings as well.
It was cruel, perhaps, to ruin so many lives, but it was all done in the name of the greater good.
He knew Jon would kill her, if she went insane, and so he made sure her mind became a maze she'd never be able to escape of alive.
It was a pity, ruining his brother's life, but it had to be done. Perhaps, in time, Jon would find happiness at the Wall. At least Bran hoped he would.
He was King now, just as he had planned it, long ago.