Because the people settle there. The land was "empty", like it was "empty" for the settlers in the Americas. See first synonym below.
settler: noun
a person who moves with a group of others to live in a new country or area.
"the early European settlers in America were often fleeing from religious persecution"
They are the path of least resistant yes. But that path often leads to collective losses, or if the stakes are high, like in climate change, to collective destruction. We get stuck in the Nash equilibrium of a prisoners dilemma.
But the point is that it doesn't matter if there is oil shortage or not. Even if there would be oil shortage, it is not (and should not be) the main reason why we're moving away from oil.
The problem is not oil shortage, because there is no oil shortage. The shale boom gave the US plenty of oil and gas to pump up. And there is plenty of coal too. Enough to last us for at least several decades. The problem is that, in doing so, we would destroy our climate.
I'm under 37 and also scratching my (European) head. Is this one of those insane US things?