If the engineers didn't know it would fail in 20 years from material fatigue, that's something that should be learned.

They may be blameless by any reasonable standard, but knowing how/when something will reach end of life is an important part of design. We learned a similar lesson with airplanes.

20 years is a very long time for a structure under such extreme stress. You can bet that this accident will influence all such designs and cause a structural review of every other large tank made of acrylic in the world, as well as various under water tunnels in large aquaria.