Parents are much more likely to have nachas from their children if they pay tuition and send their kids to yeshiva because they understand the the importance of a proper Torah chinuch. They are less likely to find their kids breaking the Torah’s rules if they keep those rules themselves, not because we have to follow society’s rules, but because they are the Ribono Shel Olam’s rules (given to us for our benefit), and out sense of gratitude to Him for all He does for us, we wish to and must.
Just to nitpick (and clarify), I can’t imagine you think that not paying tuition is going against the “Ribono Shel Olam’s rules”. Sometimes, it does happen, that a child’s parents can’t pay in full, and the school gives what they call a “needs based scholarship”. This may even be for the full amont of the tuition, and assuming the family is actually needy, they should take the tzedaka so that their child can attend Yeshiva. Please don’t insinuate that taking a scholarship is Assur (Even though I’m sure that’s not what you meant, it could be read like that).
DY has a very good point. IIRC, Rav Moshe said the reason why the generation of the 30’s went off was because the parents came home after being fired for not working on Shabbos and said “Tzu Shver Tzu Zain a Yid”, or “it is hard to be a Jew. The children internalized that being a Jew is difficult and therefore not worthwhile.
The new “Tzu Shver Tzu Zain a Yid” is tuition. And those who pay in full and those who are on scholarships both can have the attitude that “it is too much” (because it is too much, for almost everyone).
Also, paying tuition does not mean the child will graduate. Let’s say he simply failed out. Or easier, (CV) brought in a cross and tried to missionize?. He certainly should be thrown out, tuition payments notwithstanding.