Because the people involved weren't good at their job...? We've been over this multiple times now. It doesn't seem like it should be hard to figure out. What do you continue to miss?
> but they are not engineers
Sure, software involves lots of different types of work. Engineers are just one tiny piece of the puzzle. But design is exclusively the domain of engineers. Anyone working on the design is an engineer, by definition. That, again, does not imply that they know what they are doing, are good at their job, or bold enough to push back against out-to-lunch stakeholders. Having someone doing engineering work does not magically mean you are going to see an excellent product on the other side. Most people are pretty lousy at what they do.
You, again, increase your chances if you involve PEs, but that's not a job, just a designation.