most of the population live near the coast and we don't have the transmission lines to move the power from the flat, dusty interior to the coast. offshore wind is naturally close to the existing load and developers don't have to deal with as much NIMBYism related to transmission. (just the wealthy coastal elite who don't want to see them)

it must be noted however, NM just did exactly what you're talking about with a massive on shore wind project (with lots of federal help, Joe!) and it's amazing. so it's just hard, but not impossible?