Maybe it just takes longer for the market to react. Selling farming equipment has a local component to it: you need local dealers and a robust service network. Countries also tend have protectionist policies about the market, since farming is of strategic importance. All of this slows down the expansion of competitors. Add to that that the average lifetime of farming equipment is very high.

The ~10 years that John Deere has shown this behavior might just be too little for the market to adjust.