The policy of encouraging safety measures is the primary reason for the rule. Many states have similar rules. However, there is an important exception recognized by California and 14 other states. The evidentiary rule in California is limited to negligence cases. In strict liability products cases, the subsequent remedial measures are admissible. California courts addressing this issue have held that excluding evidence of remedial measures in the strict liability context would be contrary to the public policy of encouraging distributors of mass-produced goods to market safer products. Schelbauer v. Butler Manufacturing Co. (1984) 35 Cal 3d 442.
Evidentiary rules on this issue vary from state to state. If you have a subrogation case that involves a product, it is worth checking into the evidentiary rule in your state on this issue. The following states allow admission of subsequent remedial measures in strict liability product defect cases: Alaska, California, Colorado, Connecticut, Georgia, Hawaii, Iowa, Massachusetts, Missouri, Nevada, Ohio, Rhode Island, South Carolina, Wisconsin and Wyoming.