Because they likely use metrics which highlight how many criminals where caught due to their system. On the other side a metric which says how many times no co

Because they likely use metrics which highlight how many criminals where caught due to their system. On the other side a metric which says how many times no conclusive evidence was found with DNA testing sounds more like a metric of failure (but is not, if you don't have qualitative good enough evidence including "complete enough" DNA you should not make up results which simply don't exists, but then courts ruling without conclusive evidence isn't that rare and some would say even necessary to some degree. It's just that many believe DNA tests are somehow unfailable perfects ways to prove the presence of an specific person at a specific place, but they are often not).