They may be worried about political reprisals and investigations. For example, Humana faced a federal investigation when they sent out a mailer with statements

They may be worried about political reprisals and investigations. For example, Humana faced a federal investigation when they sent out a mailer with statements that contradicted claims by Senator Baucus. (http://www.msnbc.msn.com/id/32954068/ns/politics-health_care_reform/ http://www.msnbc.msn.com/id/32954068/ns/politics-health_care...)