This isn't even remotely true. The costs of a security clearance investigation are borne by the sponsoring agency, not the contracting firm. The problem is that it's difficult to justify taking an uncleared person and submitting them for a clearance. You have to have a billet where someone isn't needed to hit the ground running, you have to be willing to take the risk to hire them with the possibility you may have to fire them within 12-18 months if they don't pass the investigation, and the program and/or contracting officer they're assigned to has to be willing to sign off on it (many contracts are written such that pre-cleared individuals are required to staff it).