PBA: I’m not saying there’s a comparison with the IDF, but just from the Torah standpoint, if the kohen mashuach milchamam told the “yarei verach leivav” to leave, then that would leave the tzaddikim, who are probably (if you really want to use modern terminology, which I don’t think is the best idea) closer to the chareidim.
Most people left because of the whole “aras isha…”, “nata kerem…”, “banah bayis” thing as well as “yarei verach leivav” – this would logically create a very finely selected troop of talmidei chachamim.