The first half of the story is that the stakeholders wanted an over-the-top bridge design, complete with fake cable stays, and out of hubris decided they would use an all-concrete single-truss Accelerated Bridge Construction (ABC) design because all-concrete would look better and the university's (FIU's) engineering department sort of specialized in promoting ABC.
What could have been a much cheaper nice looking normally-designed bridge (which would be open today) ballooned (or you could say, was hijacked) into a $10mm+ bridge disaster that would be comedy if people hadn't been hurt and killed. A majority of it was even paid for by federal grants.[1]
This is why we can't have nice things. They were so focused on building a nice looking bridge — and meeting deadlines — that they didn't/couldn't allocate sufficient resources to verify the design, verify it was built and moved into place correctly.
[1] see page 9 of https://www.transportation.gov/sites/dot.gov/files/docs/brie...