Because he thought is was in the best interests of those boys.
From the story here:
Despite increasing pressure from gay rights advocates, Exxon has refused to create a specific policy barring discrimination against gay employees, as many Fortune 500 companies have done. Nonetheless, Tillerson was instrumental in lobbying the Scouts’ board to accept openly gay youths, said John Hamre, president of the Washington think tank Center for Strategic and International Studies, of which Tillerson is a board member.
“I can’t get into the intimacy of these conversations. But he agonized over this. He prayed on it, and ultimately he came to the conclusion the only thing that can guide him here is what’s best for the young boys,” he said. “I think he became a key leader in helping the group come to a consensus.”
