Iran getting nukes is a world issue, not an exclusive Israel issue. The fact that Israel is as often on the first line, does not mean that it is not a problem of the whole free world that should be solved by the whole free world. Meantime and unfortunately, the IDF have a lot of other issues to deal with. But your question is a good one, just should it be slightly changed to "why not the german, french, russian, canadian, italian, ... armies?"
Islamic State destroys part of Syria's Temple of Bel, monitoring group says (Reuters)
from the article: Some 200,000 missiles aimed consistently at Israel, top IDF officer says