That's a big problem of government mismanagement, for them to write a blank check to private contractors and then sit back and do nothing. The Apollo program went from a pipe dream to putting men on the moon in 9 years with 1960s technology like slide rules and rope memory. But making an updated jet takes 30 years somehow.
The difference is that NASA had strong managers and strong engineering expertise, so they managed contractors closely. NASA engineers worked with the contractors at every facility, and would find problems early. Then NASA would help the contractor and also pressure the contractor to get their act together. If that wasn't enough, NASA even insisted on management overhauls inside the contractor if the contractor was not performing up to snuff. NASA also did exhaustive testing of every component themselves, catching flaw that the quality control of the contractors did not catch.
For critical, super high cost projects, the government needs to closely manage contractors to keep the costs under control and the project on schedule.