So, I don't know how not to boarder politics with this post; but I'll try not to just dive straight in:
Part of this is labor; a manufacturer can deal with the pay side of it, but mixed in with all the other stuff, got to hire 5% wheel chair, 10% deaf, ect and provide 'reasonable accommodations'; it costs a fricking ton; BUT don't ever believe the work force in Mexico are being paid slave wages; they probably are around $10-15/hour
Regulations; think of the BS a large manufacturer has to do just to run a large scale, production, paint or galvinizing operation; the environmental controls, the testing, the OSHA stuff; I'll bet they have to have a dozen or more safety and environmental folks, if a guy spills a gallon of hydralic on the concrete
Profit; if they can't make a good profit, with US regs, labor, and taxes; would you prefer they just stay till they go bankrupt? They have an obligation to their shareholders, not the US gov, or US citizens; JD and every other major Corp has stock holders from around the world; and they should have the same loyalty to a US stockholder as a a Chinese or German, or whatever.
Nobody is going to pay 25% more for a high cost item cause it says made in USA. Maybe a couple percent, or maybe a 25-50% on small cost items; but not $125k for a $100k item.
Shipping; Mexico isn't really any harder to ship from than the US, and in someway, it's easier; there is some kinda law about having to use US ships with US crews to ship from US port to US port; However, you can use a Fillipeano crew, on a Liberian ship, to go from Mex to Tampa; and that's not just money, it's availability;
Also, not sure if this applies in JDs case; but if they are looking at their existing facilities, it can be better/cheaper/faster to start over somewhere new than rehab the existing facilities. relocating a facility as Huge as JD needs, would take years and years of public meetings, endangered species surveys, impact fees, permitting, ecr. Probably would be a maricle to have a facility up and running in 5 years relocating in US.