Offshore oil rigs deal in billions of dollars worth of hydrocarbons per day. The revenues make it feasible to offer high salaries and still generate massive returns. Many rural locations just aren't economically productive to justify the kinds of salaries necessary to draw people to them.
Why can't the farms increase prices to support a basic quality-of-life for those living there?
I don't disagree there's some breakdown of the market here, but I'm not sure that saying "well there's not enough money coming in to the area" isn't stopping a step short.
In that setting, the "regional" middlemen have the power to set prices, not the farmers, so a distant farmer from a poor community has no leverage over what teachers are paid in their community.
Generally speaking, I think almost all locally-produced, distributed industries work this way, by aggregating many producers the middleman has a ton of power to set prices, but of course is subject to the prices set by the next tier up, all the way to the commodities exchange, from what I can tell.
Anyway, this "averaging over a large area" ruins local economic efficiency.