The bunker sand installation detail often calls for 6 inches of compacted bunker sand uniformly placed throughout the bunker floor. Uniform sand depth is critical to the bunker playability, if the sand gets too thick, you will get a puffy lie, and if its only a few inches thick than the ball will bounce upon impact.
This depth gets compromised by golfers, wind , rain and constant turning of bunker raking machinery. Insuring that surface rain flow from adjoining areas is diverted around each bunker is critical. These impacts combined with golfer demands for clean, raked, weed free bunkers require that you need to keep them pretty, hence the 9 person crew.
Those shaggy faces and surrounds can get to be a maintenance issue also. The fescues blowing in the wind can be impacted by invasive weeds, insects, burrowing animals, insects, and golfers walking all over them. They require minimal amounts of water and fertilizer, and can be adversely impacted by irrigation over spray and chemical and fertilizer toxicity.