Chargers won the division 5 out of 6 years not too long ago, so it isn't like they are have been bad for a long time. Having their entire team minus Rivers on IR every year is pretty unlucky though.
AFCW is actually pretty competitive overall too, 5 different teams have won it in the last 18 years even with the Chargers, Raiders and Broncos all going on runs in that time frame.