I think everyone thought the stock market would go up 10% a year forever.
That is what happened in states like Illinois. On paper, they were close to being 100% funded before the Nasdaq implosion at the turn of the century. During the big run up they quit making the employer contributions to the state pension systems. When when the SHTF, they borrowed from the pension plans and have never recovered. If they were a private business, they would have been required to make the employer's share of SS at all times.