I've seen lots of people in the past asking why the Romulans stuck to the treaty after the Federation broke it, many seem to see it as a plothole. But really when you think about the realpolitik/~~geo~~ galactic politics of it, it was a massive win for the Federation.

If the Romulans said "Hey this is bullshit! Our treaty is over!" then the Federation would just say "aight lmao, we'll just use this cloaking tech that's way better than yours. And it can be trivially retrofitted to existing ships, our whole fleet will have this tech."

By flexing that they can make this tech, it made clear to the Romulans that sticking to the treaty was something that was absolutely within their best interest, whereas before they weren't so sure about that. They thought they had a technological upper hand and were being hamstrung by their inability to fully leverage it to crush the Federation.

Bonus: it showed the Klingons that they too shouldn't provoke the Federation too much, nor should they try to destabilise relations between the Federation and the Romulans either, because if that treaty dies, they'd also lose what they thought was an advantage they had as well.

The whole thing was a staggering power-play by the Federation. They fulfilled the Speak softly and carry a big stick mantra perfectly.