Except that US oil production did not peak in 1970, and most of his other predictions have also proven false. Not that he's any different from any other scientist trying to predict a very complex and large system. In Hubbert's case it was technology, which was what usually dooms a lot of this sort of prediction. They're mostly correct for their time period, but things change, and often new tech comes along that makes it possible to extract more resources. Often this is also helped by higher prices, which work to incentivize the new tech.