Teribus, you're right - a number of factors must be weighed in deciding who should get a govt. contract. However:
- not all contracts are for military projects
and
- when competitive bids are submitted for one project a number of companies probably get vetted.   It's probably not necessary to start from scratch for everyone when a new project comes up.
- it would probably be a good idea for the govt. to keep (current) records on a number of potential contractors, both in terms of competence and in terms of security, just so no one company can take advantage of lack of competition.