because MLB equates more scoring with happier fans.
also, most MLB fans dont bet on the games, so having those late inning relievers suck gives them hope that they can make a comeback.
i dont think MLB cares much about the watered down pitching.....
frankly, the problem lies in every sport. it's why Martin Grammatica still has a job. it's why Aaron Brooks started for the Raiduhs last year. it's why Chris Webbers one-legged self is still playing and why Luke Jackson makes millions.