The Chargers owner did this all himself.
While never a rabid sports city, San Diego still had a large loyal Charger's fan base until the team moved to LA.
The owner, Spanos, wanted a free stadium and wanted San Diego to pay for it. When they wouldn't, he moved the team to LA where he could play in the Ram's upcoming stadium, which was already fully financed by the Ram's owner.
The fans didn't follow. Moving a team into the already oversaturated LA sports market was a bad decision. Refusing to spend some of your NFL profits to fix your existing stadium, was a slap in the face to the fan base spending hard earned money on the team.
The chargers get what they deserve.