In this case because they are positioned to become a form of role model of these students. Who will eventually find out that their favorite company can be horrible to negligible consequence.

You could justify almost any such attack like this. Can you not just appreciate what you’re given here for free, for once? The effort people have put into this? Just imagine pouring months into something like this and getting your post as a thanks.

Because they still benefit. They benefit when people consume their products and they benefit when they're given a forum within the community.