TL;DR, this was a triumph of stupidity and greed over good engineering.
Engineering design standards are often written in blood, in the sense that these standards often came into being after accidents involving serious loss of life. The CEO of Oceangate ignored them, apparently because they got in his way of saving costs. As it turns out, reality is not susceptible to CEO bullshit.
Unsurprisingly, “move fast and break things” is not a good strategy when lives are at stake.