Europe calls our bluff on language
Another view was that the Irish were just not sufficiently interested. Whichever view is correct might be ascertained under the 30-year rule, following a request under the Freedom of Information Act.
In fact, Irish negotiators gained recognition for the Irish language in the official texts of EEC (later EU) treaties, since the wording of these might require amendments to our national constitution, where the Irish version over-rides the English in case of doubt.