^
And I have to wonder why that is? The Romulans had put time in, they had been in some very good TNG episodes, but if I recall Rick Berman never cared for them. In TOS and especially TNG the Klingons were better fleshed out, but we never really got a deep exploration of Romulan culture. It's like, we'll we need a bad guy, insert the Romulans.
The Romulans did have distinctive ships and uniforms, but they never got much of a distinct culture. To me, they were interchangeable with the Cardassians (at least the early incarnations with the Cardassians). Though the Cardassians had a more unique, intricate design, and they also had distinctive ships, uniforms, and they even had distinct (recent) history due to their occupation of Bajor and even their war with the Federation, which wasn't explored much, but it's there. And I think DS9 went more into developing them, but the Romulans never really got that. DS9 went on to do great work with the Dominion as well, and didn't really 'need' the Romulans. And DS9 continued fleshing out the Klingons. VOY to some extent did as well, and to a lesser extent so did ENT with the Klingons, when the Romulans made far more sense during that time period to feature as bad guys, even if the heroes didn't knowingly interact with them.
I have to wonder since Berman Trek (with the exception of ENT) largely minimized the Vulcans that that took away an interest in exploring the Romulans more. With the Romulans being the dark reflection of the Vulcans, perhaps they lost something if there were no prominent Vulcan characters on TNG or DS9 and Tuvok on VOY, being lost in the Delta Quadrant, removed the exploration of the Vulcan/Romulan duality as well. TNG did replace that to some extent with Worf's enmity toward the Romulans, but the show didn't do much to use Worf's tragic relationship with them as a spring board to explore Romulan history and culture. The major time we got that was in "Unification" with Spock's mission to Romulus. And to a lesser extent in that episode where Geordi and the Romulan soldier are trapped. We got some good insight into the Romulan mindset and also Worf's feelings about them as well.
To me, it was like, okay we need a bad guy here and we already got Romulan ship models, costumes, wigs, and weapons, so just slide them in. Plus the audience knows them and already know they are a formidable adversary so we don't need to create someone new, is how I wonder if why they used them in some of those TNG episodes. If the Ferengi had actually turned out to be seen as legitimate threats it makes me wonder if we would've seen the Romulans as much, or at all, as we did in TNG.
So, if Berman didn't care for the Romulans and there wasn't a lot of 'there' there when it comes to making them stand-out (even from a visual perspective, they still look like Vulcans, despite Berman's attempts to differentiate them), Berman, Braga, and Logan, might have felt that the Romulans weren't interesting enough or threatening enough to be legitimate bad guys. I disagree. Though I liked the Remans and the Son'a for that matter, the Romulans were great villains and deserved more of a spotlight. I remember being thrilled just by seeing even a dead one in GEN and wish they had followed up on that. Though I liked the Son'a, I wish they had gone with an earlier idea to make the main bad guys in INS the Romulans. It would've raised the stakes big time.