Perhaps because they realize the difference in outlook would bring marriage problems? Would you be interested in getting married with someone who dismisses what is valuable in your eyes and who greatly values what is irrelevant in your eyes? I wouldn’t and most people wouldn’t. Most people see marriage as building life with our soulmate, the one we agree with in regards to important life issues; most people do not use marriage and relationships in general as a crowbar to get our partner to change and assimilate (that is not our way, it is what some nonjews do).
People who wish to do national service or military service should be able to do so, whether or not they realize the reality is quite different from brochures and advertising. I have never tried to dissuade anyone from enrolling in either, although, of course, my children and close family I definitely would. This has nothing to do with the discussion at hand, ie the attempt to force into military service or national service, people who do not want anything to do with it.