Israel's population is to small for a professional army, they are luxuries of big countries where the populations are in the tens if not hundreds of millions. Israel has a population of around 7 million you take out the arabs that takes it to about 5.6 million, then take out the sick and your down to about 5 million then there is the children who are to young and the people who are to old and already the number of people eligable is small and from that small group you have to enough people who want to chose the military as a full time career. A professional army is the ideal choice because but in Israel its not practical.
Islamic State militants blow up ancient Arch of Triumph in Palmyra (Reuters)
from the article: IDF is no longer the people's army