This is also the result of the continuing skirmishes in scope wars and the inability of airline management and labor to work together more effectively. If you assume that there is a reasonable amount of demand for airframes in this size bracket, priced appropriately (which Delta seems to have proven with their 717 fleet, and a number of foreign carriers know), then (a.) Airframe manufacturers gotta build 'em, and (b.) Airlines gotta acquire 'em, and (c.) Somebody's gotta fly 'em. We can't wait for un-manned cockpits to solve (c.). Grow up and figure it out, folks. Most of the rest of the world doesn't have this problem (or at least, to this extent). There are also three other manufacturers in Japan, China and Russia making aircraft that overlap these size criteria.
Eclipse's comment about Airbus sales does need to take into account John Leahy's impending retirement. Leahy has been able to sell ice boxes to Eskimos (if not to Alaska Airlines), and no heir seems to be immediately in sight.