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Because not many baseball players like Seattle specifically.
Baseball is an increasingly latin pursuit...the American player pool has shrunk considerably...and the Northern origin ballplayers are even more rare (the types more likely to want Seattle than, say, LA or Atlanta or DC). Seattle is way out in left field...no one expressly WANTS to play here except losers who don't like the limelight. So...yeah...enjoy losing a lot...because that's what you'll do.