I could see that the exaggerated capabilities of law enforcement/national security organisations (CSI, NCIS etc etc) could be effective as a tool to reassure the public into thinking they’re well protected, and possibly even deter some would be first time/amateur smalltime criminals since they might feel comitting some petty offence isn’t worth it because they’ll definately be caught out, but as you say a professional criminal, whether they’re an NCIS viewer or not, isn’t likely to be too put off.
But as also mentioned, I think it might be an element of reality just not being exciting enough. You’re probably not going to be as thrilled by a show where everything’s a bit like your own work life, everyone’s fumbling with equipment past its best, being told there’s no room in the budget for anything better, it takes ages for some important thing to get done and even then the results might be disappointing, they sometimes get stuff wrong and have to go back and correct their mistakes or just live with the consequences, (although as you say there are all those harrowing Cold Cases, and sometimes they do fail in some dramatic and spectacular way that involves major story twists or something,) and interdepartmental or organisational squabbles leave everyone feeling cheated and bitter.
I think there might also be an element of wish fulfillment. The hero characters of these shows are often characters lots of us would love to be like. Always understanding and knowledgable, generally know the truth straight away, and can always trust their instinct, always gets the job done, etc etc. So as part of that, they of course have to be able to find case-breaking evidence right in the nick of time, analyse it in the space of a montage with the click of a button, break some impenetrable puzzle, stop a fleeing bad guy with a single well aimed shot, and all while getting the better of all the interdepartmental/other organisational rivals who’d like to see them fail. It’s how we’d like to be in those situations.