If everybody in the US were to exercise more 5 million lives would be saved as well as $50 billion in healthcare costs. So why are people sitting on their butts?
We have evolved to avoid pointless physical activity when calories were scarce and our finite energy went into hunting the food we needed to survive. In a privileged developed country, such as that in which I write this, our lifestyles on average no longer necessitate much activity. Without that requirement a lot of people simply don’t get enough movement.