There is a more pressing reason that has pushed farmers to continually buy new equipment. Farm credit services pressures farmers into this practice.
When giving out a loan for operations, a farmer's ability to pay is heavily weighted on farmers having newer equipment. The excuse that I have heard for the bank to do this, is that the bank can't easily tell which farmers take better care of their equipment, thus favoring the newer equipment across the board.
The agents working directly with the farmers advocate for this, as there are internal incentives for making larger loans.