It's partly a matter of location. It works where you have fescue or Bermuda fairways, because it's not much more expensive to maintain those at fairway height than as rough . . .
Maybe this is site specific, but having 2-3 times more fairway height bermudagrass is most certainly "not much more expensive to maintain" than rough.
These extra areas require the same fertility, (think a $15-$20k fertilizer application x 2 or 3) cultural practices, same spray packages. These are areas mowed 3-4x week vs 1-2x. These areas get aerified 2-3x a year. Think about topdressing 30-35 acres of fairways vs 70-80 acres (or more) of shortcut. (Extra $50k in sand?)
They also require twice as many fairway units. Most golf courses have 3-4 units @ $100k each. Now you need 7-8 or more. This also means 7-8+ people are needed to complete mowing 3-4x a week vs 1-2 rough units 1x a week. There is also a maintenance piece were sharpening a rotary blade 1x a month (rough) vs having to check an extra 20 reels 3x a week.
Certainly, here in FL, having 2-3x more shortgrass than the "normal" course is not cheaper by any means. Please understand, this isn't a knock on the look-its tremendous, but it's not a cost that is just swept under the rug.