They weren't practicing due diligence. The charges and suits are based on the years where tests were available and the people in charge knew the blood was potentially contaminated, but made the choice to continue sending it to hospitals anyway. Then when infected people started showing up, they delayed tracking down the donors.

There was a major inquiry (the Krever Inquiry) that went on for years. As a result of the findings the government took control of the blood supply completely out of the hands of the Red Cross.

has been completely taken away from the Red Cross as a result of what happened, and the way blood and donors are tracked is a lot tighter now.