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.

People who say yes without questioning their superiors or clients tend to get promoted.

This is what I assume they mean.