Even if cost them the same $ to run a team as it would have to keep with the former CSC team having your top rider place 20 spots down and not winning as many races will cost more in the long term with fewer bike sales.
Imagine if they had stayed with the former CSC team and Fabian had won on a P4 today. Cervelo would have been cranking out the PR and that translates to a high number of bike sales. Right now they are showing that the P4 is no better than any other bike