Agree that "mismanagement" is probably not the right word, I think that they were probably taking a calculated risk that the economics would work out in the end.
The core of the business was executing on cheaper, more reliable buildouts. SMRs might even be more expensive per watt than larger reactors, and that could be OK as long as it was cheap enough, and led to project sizes that were smaller than $20B and had much smaller chance of project failure.
Certification is useless for a design that's too expensive, as that was half of the core value proposition. (With the other half of the value proposition being smaller risk.)
Right now it looks like a core gamble of the company has not paid off. It's unclear if they can learn any lessons from the cost increase that would let them come up with a cheaper second design. But I'd suspect that the founders were just wearing rose colored glasses for their first cost estimates, with the hope that some future innovation would let them meet unrealistic starting targets, and it hasn't happened yet.