Why don't members of congress from both parties "argue" with the reports and reviews submitted to them by the cbo?

 Because the CBO is non-partisan and unbiased

The CBO is a federal budget within the legislative arm of the USA congress. in force since 1975, it has been reputed for providing independent budgetary analysis to assist congress in performing its fiscal function effectively. Its employees are strictly non-partisan and are hire as per competence basis.