Because the company offered millions of dollars to the suvivors to settle out of court so no details would come out. Most of the suvivors had received a settlement from their life insurance companies, so they were not hurting for money.

What they were hurting for was little bit of truth and open court was the best place to get it.

By the way, in the aftermath of the court cases the CEO of the company retired and hundreds of managers were let go.

To this date there have been few improvements in the safety of oil refineriy operations.