It was more than just re-purposing the show to cable. USA's television production unit took over the responsibilities of Criminal Intent -- and while USA is part of the NBC Universal corporate umbrella, it has its own financial structure and budgetary realities (one of which is that it certainly doesn't have the money to throw around that the NBC broadcast network does).
The move to USA brought a lot of changes to Criminal Intent, the biggest of which was the budget, which was slashed and burned about in half.
The changes in Criminal Intent were noticeable, too; scripts were being rushed into production, high-profile guest stars stopped appearing with regularity, and then cast changes started coming, with Noth being dumped after the seventh season followed by the housecleaning between seasons eight and nine -- and now the recent seasons have been slashed in length, too, from 20-plus episodes to 16. (Granted, Criminal Intent brought some of its own most recent budgetary problems on itself, when Goldblum's first two episodes were tossed and re-shot, a few more scripts were abandoned and Robert Nathan was sacked.)
I don't work at USA, so I can't say for any certainty what would happen to Law & Order if USA were to take over its production, but I doubt we'd like it. Waterston would almost certainly be gone, and who knows what other cast changes would happen? Season lengths would undoubtedly be shorter and any elaborate location shoots would go out the window.
In any event, it doesn't make sense for USA to pick it up. When it grabbed Criminal Intent, it was filling a niche on the channel that was wide open (and the series had the goofy, manic Goren character, and now has the goofy, manic Nichols character). USA's entire programming mantra, nowadays, is "Characters Welcome." I don't see that jiving too well with the "character-proof" mantra that has been Law & Order's calling card since its inception. Furthermore, with Law & Order, it would have two essentially identical shows (one has a half-hour of lawyers, one doesn't, and after that the only difference is casting), one of which (CI) is borderline in popularity, and the other of which has become a ratings albatross in the past year. I'd hate to be a fly on the wall for that meeting.
"We're supposed to start producing another show in New York? In addition to the one we already have? And this new show's pretty much the same show as the first? And no one's watching it on its current channel? Yeah, that's a great idea, sign us up."
TNT is in a similar boat; it just doesn't have the money to throw towards a bunch of additional original drama programming when it already revamped its schedule to focus on such programming, and then made a late decision to start producing another year of Southland -- as opposed to just picking up already-completed episodes of it. (NBC's offer for Law & Order was, supposedly, "In addition to re-upping our deal for re-runs, are you interested in forking over a chunk of the production cash?" Why would TNT agree to that?)
I mean, it sucks. Law & Order is a Monday evening fixture, and I watch the weekday re-runs on TNT religiously. But it's been in a perfect storm: The ratings have become abysmal (partially due to NBC's schedule muckery, partially due to the show being 20 years old) and if NBC can only keep one L&O, then SVU is the only one that makes sense from a financial perspective; TNT almost certainly doesn't have the money to buy it and keep it going; it makes absolutely zero sense for USA to produce it.
Other people have already said this, but I'm not even that bummed-out anymore about there not being a proper series finale. The entire theme of Homicide: Life Everlasting (rather ham-fistedly delivered) was that death, and life, go on and on. That's been the point of Law & Order since the start: Cops and lawyers come and go, but people will always break the law, the police will always catch them, and lawyers will always put them in -- or try to keep them out of -- jail. That point has been made for 20 years. The show doesn't need to awkwardly bring back old characters or assemble a Very Special Finale to make that point.
