1. If the Israelis wanted a large number of Hareidi to sign up, they could make the army friendly for frum soldiers in ways that would not impact on the military matters, such as a rule requiring all soldiers to observe the laws of yichud and negiah and a strict “non-fraternization while on duty or on base” policy. They could run the army like the handful of segregated frum units in terms of leaving time for davening, kashruth, Shabbos. They choose not to. However if they made the zionists institution “frum-friendly” it would radically change Eretz Yisrael and alienate the secular zionists who run the state but are increasingly unwilling to serve in the army.
2. Perhaps 10% of the yeshiva students are anti-zionists (who refuse to accept zionist subsidies). If the army tries to draft them they will resist and trying to arrest them will seriously hurt Israel’s image and undermine the argument that it is a Jewish homeland. It is better politically to say they are to busy learning to serve in the army rather than saying that zionism is apikorsis. Drafting the yeshiva students would turn Neturei Karta into a serious political movement, with its membership being measured in thousands rather than dozens.
3. Drafting unwilling, unhappy and disloyal soldiers is a good way to undermine the ability of the army to defend the country. Repeal of the Tal law, meaning conscription of the yeshiva students, is probably the Palestinians’ best chance of getting a state with Jerusalem as its capital, and Yaffo-Tel Aviv as its largest city.
4. Of course, for those of us who believe in HaShem and His Torah, we know that in fact it is the yeshiva students, who show tremendous mesiros nefesh in giving up any chance of a middle class lifestyle to learn Torah, who are really the ones defending Eretz Yisrael. If the government closes down the yeshivos, and forces the Hareidim to flee to other countries, HaShem will probably close down the zionist enterprise once and for all. But that’s only background to the above debate.