* Most of the people involved had some familiarity with written and liturgical Hebrew already.
* The revival was kicked off with a seed population of self-selected, ideologically-motivated Zionists in-country.
* When that seed of fluent speakers spread it to larger waves of immigration, there was no alternative lingua franca.
Italy was also a case where there was no alternative lingua franca, and it was in fact a dialect which was both mutually-intelligible with extant dialects, and was in fact made official in many Italian states well before unification.
More generally, these both are exactly in line with GP's point: "people are motivated to learn a language when it has prestige". Both languages were absolutely high prestige at the time.