I went to two Sonic games in the mid 2000s. I like basketball, but seeing the sport in person was expensive as I recall. I remembered a good portion of empty seats, too.
Seattle sports fans just don't stick around if the team isn't winning. See: Safeco Field circa 2001-2003 and Safeco Field now. It's packed for the Yankess and Boston, but generally they aren't pulling numbers anything like they were a decade ago.
Also, Sacramento did more to keep the Kings than Seattle ever did to keep the Sonics. I say let them have their only pro team and follow Portland if you're particularly desperate.
Can say that about 95% of the pro sports teams in this country.
And no denying that the city didn't do shit to try and keep the team, but that shouldn't be held against the fans, who had no say in it.