I just finished reading the Lost Era novel, Serpents Among the Ruins, last night. It dealt with the Tomed Incident and the subsequent Treaty of Algeron.
***Minor Spoilers from Novel***
In short, the Federation had no true interest in developing cloaking technology but gave the appearance of pursuing it in order to gain a treaty concession, namely that the Romulans withdraw from Koltaari, a planet they had recently occupied. Though not an onscreen answer, it's an answer.