I'm sure Tomalak relished the chance to do away with Jarok (surely they were longtime enemies) but Jarok's fall from grace was orchestrated by pretty much the entire Romulan military.
Tomalak just got to deliver the goods, so to speak.
Well, I admit I'm off on a theory here, but I kind of think Jarok's fall from speaking out about aggressive actions really only took the form of having been censured & posted to penalizing or at least to distant & less significant assignments etc... all of which surely would've had to have been going on prior to the events at Galorndon Core, 2 episodes earlier, & probably something that was known quite well around the water cooler, but I mean griping & condemning command doesn't necessarily speak to traitorous intent. It's just dissent, & gets treated the way he had been
However, the plan to oust him as a traitor by feeding him bad intel had maybe only been going on recently enough to get him to take immediate drastic measures, & could've been spearheaded by a power-hungry or desperate party like Tomalak, in their ranks, with a current blemish, & something to prove. That it would be Tomalak & Picard to end up face to face once again is just too coincidental for him to not have had some motive in play.
So, while in reality, the show likely just had 2 really good Romulan scripts, & a recently new stellar actor to bring back as their Romulan bad guy, the way it plays out kind of lets me play with a little head canon, & think that when Tomalak got humiliated at Galorndon Core, he had to face some music back home, & his scheme was to pitch a face save, by luring a Starfleet ship to crossover in the Neutral Zone, the way he'd been caught doing recently, by throwing out a bone they'd been trying to deal with already anyhow. 2 Birds, 1 stone.
I mean the whole scheme's motive was purely to get a Starfleet ship to violate treaty by entering the neutral zone. What's the impetus of that besides that they themselves had just recently been caught doing that very thing & got bad PR from it, & having their counterparts do it too saves face some? Tomalak is neck deep in the controversy, & I like to think he saw a chance to save face for himself & everyone, & a chance to get back at Picard, if they pinpointed where they let this play out, & got a chance to take down a superior, & maybe get a power grab of some kind for himself too.