“The roshei yeshiva of YU, just like HaRav Aharon Lichtenstein, shlita, endorse fully service of all bnei torah in Tzahal. See Sotah 44b.”
Most modern Orthodox don’t want to serve in the IDF. They want to make money in America. Why live a life of sacrifice when it is so much easier in America? If they decide to make aliya, it is only after retirement. Many American chareidim want to make aliya right after they get married so that they can learn in Israeli yeshivas. They are prepared to live a life of sacrifice. This aliya will now end.