the goal of a yeshiva is not to make money but to study torah.
The reason is that Torah study leads to following it "if you will walk in My statutes.." (Lev.26:3) (which refers to torah study. see Rashi there).
and lack of torah study leads to abandonment of it and God (see Lev.26:14): "But if you do not listen to Me and do not perform all these commandments", which refers to Torah study (Rashi), then the cascade of abandoning everything follows as explained there.
See also the Path of the Just where he explains the Baraitha "Torah leads to watchfulness..."
and in ch.5
For the Creator, blessed be He, who created the evil inclination also
created the torah as its antidote as our sages of blessed memory have
stated: "I have created the evil inclination, and I have created the
torah as its antidote" (Kidushin 30b).
Hence, to us torah study is of utmost importance. For it produces torah observant Jews and the lack of it produces Jews who drop out of Judaism. In the past few centuries, especially where Jews left the ghettos and mingled with non-Jews, it became essential to strengthen this area and thus the yeshiva movement was started 200 years ago.