A coupla reasons why....
-Initial GOPian links to the study - either out of abject ignorance or intentional deceit, implied that these jobs would be lost to people against their will.
-Per the REALLY plain language of the report (and a few notable GOPs), they were forced to walk that one back rather quickly.
-That's when they switched to the angle that Obamacare was going to allow people to choose to be freeloaders and that's bad. Now I can see why a GOP might "feel" that angle. The problem for them is that clearly, the CBO's prediction of people who might choose to work less as a function of Obamacare, applies to people in their 50's, 60's, and maybe even 70's. And...you SERIOUSLY thinking branding that demographic as "freeloaders", is going to catch on with much of anyone who isn't already "all in" with Fox/GOPism?