With the standard practice where a 2nd team gets tasked with reducing code defects in existing code, with their only metric being reducing the number of defects

With the standard practice where a 2nd team gets tasked with reducing code defects in existing code, with their only metric being reducing the number of defects (that the given tools generate), without regard to the quality of the fixes, and preferably staffed with high churn rate junior developers, the outcomes are not surprising.