Oh, that wasn't meant as an justification for why.
It wasn't meant as suggestion for how to fix it. Put a JAG officer in the main cast. Have her do away missions with other crew members on planets that have established civilizations. Give her the same kind of commentary other technical and sociological characters get every now and then. Toss her an episode or two every now and then where the crew needs some obscure knowledge that falls within her purview to solve a problem. Doesn't even have to be the main problem in the same way you occasionally have Scotty or Geordie or O'Brien pop up in episodes they are otherwise uninvolved in to say they did x, y, z and the plan that the actual featured characters of the episode have in place should be good to go.
Do we really want a character to not have anything substantive to say ("Nothing significant to report, sir") among operators and the general staff... but then shoehorn in an awkward scene between her and the Captain (who is still fighting off Borg possession or worrying about deploying forces to the Delta Quadrant) that she spent hours upon hours of off-screen time researching the Starfleet regulation on promotion actions and that's why Harry Kim is still lawfully an Ensign? Or that she researched technical order concerning transporter usage, because you know that JAG is going to be leading the Equal Opportunity complaint against LT Barclay's holodeck proclivities?
Also, she's helping the random LCDR write the reprimand for the Ensign who showed up late to work because he spent too much time at Quark's.
In theory, you could have a steely-faced JAG briefing Picard that the governing Starfleet rules of engagement prohibit firing upon the Crystalline Entity because it hadn't been declared hostile by the random evil Admiral who ate a brainworm, and said Admiral withheld such declarations from subordinate commanders ... unless, nudge nudge, the
Enterprise was acting in self-defense?
Also, the JAG would totally be the one to pull together a massive chronology in Adobe Acrobat CCCLV Pro Edition for all of CAPT Janeway's timeline shenanigans, and she would spend about 72 hours fighting with the software to create a decision memo for another corrupt Admiral (maybe secretly also a Timecop).
Also, she would approve the bake sale fundraiser dedicated to the memory of Tuvix.
Maybe it could work! Let's cast the guy who plays the lawyer on It's Always Sunny!
Source: I am a JAG officer. We are not usually very interesting.