I think it is just a bit too cold to support farming. Being an island, this meant importing food and nobody may have wanted to take the initiative to try to settle a place that cold and far from other settlements for a long time. A charismatic French chocolate tycoon named Henri Menier bought the entire island in the late 19th century and worked hard to develop a community there. The town he started was starting to establish itself but it apparently wasn't able to stand on its own, because his heirs didn't share his interest in the project and when they sold off Anticosti, the whole thing kind of devolved into a small logging camp with a summer sport hunting business. Even if Menier had lived long enough to continue his development scheme or produced an heir who did as well, WWI and the great depression would have made it hard to gain traction. The key to success then, would be for a man, perhaps cut from the same cloth as Menier, to have attempted to develop his own personal island, but to have done so a few decades earlier than Menier did.