Irish is competing against English- the most valuable language for business, education, and culture- in a stable environment where switching from English to Irish puts you at a disadvantage. Irish has more speakers now than in the recent past, but they're not geographically concise so it's more of a novelty than a necessity. The only areas Irish remains dominant is the Gaeltacht where it is common enough to be used in daily life.

Hebrew succeeded because of a combination of factors that made it very lucky. First was the influx of immigrants to Israel that had no common language and little common culture outside of Judaism. While the British authorities operated in English, it was nowhere near a dominant language. So groups were settled in multicultural neighbourhoods and encouraged to use Hebrew as common language. As the alternative was being unable to communicate, the success of this initiative was vital.

Second was the culture of these early settlers. They had moved to a foreign land with the promise of a Jewish homeland. While there was some resistance to the idea (as Hebrew was a holy tongue and not to be used for trivial matters like business), overall the idea of a common Jewish language was appealing to the ideology of the first immigrants.

Third was the high rate of birth in proto-Israel. Hebrew was used in school, and a large generation of fluent Hebrew speakers appeared at once. In Ireland kids learn Irish, then never use it because all their colleagues and elders use English.

An article on Hebrew's success and history: http://www.tau.ac.il/~izreel/publications/Athbheochan_eng_La2005.pdf

An article on Irish's failure:
http://dingo.sbs.arizona.edu/~carnie/publications/PDF/Endangered.pdf