If a town has the room for expansion then they will plan to expand. It's cheaper to do this through farm fields than when the housing is already there. And most

If a town has the room for expansion then they will plan to expand. It's cheaper to do this through farm fields than when the housing is already there. And most of this will be done with the input of the land developers. i.e. They plan to build a 120 unit housing development so the city has to plan and fund a sewer and roads for 120 households. Sewer and roads are fixed costs if you plan for 120 units why not 500 it's only marginally more expensive. Now that plumbed land is more valuable. The next group of developers can do up to 380 units without waiting for sewer and roads to be built. A prospective buyer isn't looking to buy a house 4-5 years down the line. They have the money now and want it right away. Time of delivery effects the purchase price which is how cheap exurbs become pricier suburbs.