Because Abraham pulled his guys out of yeshiva and made them join the army (Nedarim 32a). The world is only held up because of Torah (The end of Psachim 68, and Sanhedrin 99). (See Jun 4, 2013: Jul 16, 2012)
We all know how hard it is to learn Torah, because the Satan will do anything in his power to prevent you from doing this great Mitzva. But the Satan does not care if woman learn Torah since no one ever asked them to learn in the first place. (See Yorah Deah 246, 6, Taz 3, and Tosfos Avoda Zara 3a). (See Oct 28, 2010)
So if you already have a guy sitting and learning Torah you shlepp him out of Bais Medrash to go to the army and work? Are you out of your mind? You know how evil this is? Only a guy who worships 2 gods can do a thing like that. The G-d of the Torah, and the god of Madda, college, and evolution.
If the Kollel system disintegrates because it cannot sustain itself that is between G-d and kollel, but to shlepp a guy out of Bais Medrash to go to work, are you crazy? Who needs work? Why can't a guy learn in poverty? As far as I know, the only generation that almost brought Moshiach was the generation of Chizkyah, where every single person sat and learned Torah (Sanhedrin 94). (See Jun 4, 2013)