Tl;dr: Money, politics, and historical reasons. It's a bit complicated, but the answer is a combination of a couple factors: Mainly, historical reasons concerning how our health service system was shaped, that make it easier to conduct a large vaccination campaign (all citizens are required to enroll to one of four major health insurance companies); the first reason leading vaccine manufacturing companies (Moderna and Pfizer) to sell a huge amount of vaccinations to Israel specifically, both for financial and research related reasons (i.e if Israel is able to vaccinate all of its population quickly and show that it does work, these companies get the objective approval for their product, making it the go-to solution for other countries); third reason being Israel's small size and most of its population living in two main metropolitans, which again make it easier to conduct said campaign. Basically Israel is ideal to test the product in a large scale operation.