It's actually even less efficient than that. On top of keeping spending high, every project that involves contractors must have at least 3 bidders [0]. So for smaller projects people often spend substantially more time modifying contract details and finding contractors than the project itself takes. (By playing with project requirements, you can increase the pool of contractors). At an unnamed national lab, 6-week projects typically took 6-18 months of hunting down contractors until the start of work.

[0] not sure if this is still true, but certainly was in 80s-early 00s.