You need to watch less TV docudrama and talk to more people in the justice system.
Cops & Defense/District Attorneys are well aware of the limitations of DNA (even though many jurors aren't)? DNA, like fingerprints mean nothing to a case if the implicated people have reasonable reasons for them being found. Do you really think DA's try to surprise the defense by trumpeting "The accused's DNA was found on the crime scene" when they suspect a guy killed his wife in their home?!? No, it's when the proof is conclusively damning like a suspect that claims no contact with a rape victim that is trumped by his DNA in a rape kit that it is useful.
However, many jurors, after watching CSI year after year, now expect ironclad scientific evidence and are reluctant to convict without it.