Ben Levi,
The fact is that the vast vast majority of Chareidim do not serve in any of those organizations in lieu of the Army. If the Chareidim were willing to accept mandatory service for all yeshiva bochrim in an org like Zaka for example then the situation would not be what it is today. The Chareidim will not accept such a proposal they want to be left alone and not have to do anything but learn if that’s what they want, while secular people must go join the army by age 18. That’s the issue.