The farmers have abandoned their homes, and the land has become uninhabited. The only things left with life in them are the modern farming implements, made of metal and fueled by gasoline. Unlike traditional farmers and beasts of burden, however, the tractors lose all vitality once they are powered down.
The mechanized, profit-hungry nature of the new farming techniques dehumanizes everyone involved. The farming process has lost the organic intimacy that it had for families like the Joads.
The cold, mechanized efficiency of these technical tools removes the land’s wonderful properties, and the tractor men cannot understand the land as deeply as the farmers did. Similarly, this machinery prevents the men who use it from truly understanding themselves, and life in general, in anything but detached, scientific terms. Meanwhile, the vacant houses become increasingly decrepit. Prairie animals take over the homes.
Once again, technology is shown to alienate men from the natural sense of wonder and intimate connection to the land that makes them human. By failing to love and understand the land, the tractor men miss out on the fundamental humanity that Casy praises above all else.