a.) they seem more representative of what most war is like
b.) the turning points of most wars actually fall during them, eg. Guadalcanal rather than Midway was the turning point of the WW2 Pacific Theater, the Battle of the Atlantic rather than Dunkirk or Normandy was the turning point of the European theater.
c.) oftentimes, the long, brutal experience of these types of battles is what led to the logistic and technical improvements that actually wins the war
Similarly, it'd be interesting to read war histories that focus on logistics and technological development. D-Day has had zillions of movies made about it; codebreaking has had one or two; and the logistics of assembling an army of millions and shipping them across the Atlantic in secrecy to land on hostile territory has had none that I know of.