Fresh ideas? the stuff they teach at university is constantly changing, it could well be that the recent graduate that you jsut hired has some ideas that your seasoned programmers wouldn't consider because they are stuck in a certain way of thinking.
Altruism, I think any company has to appreciate that we all start somewhere, and if we don't get a start then we don't carry on being developers.
Cheap labor, not only does having a graduate recruitment get your cheap labour it can also foster relationships with local universities and lead to even cheaper if not free labor in the form of summer internships (I don't agree with not paying them though).
Not paying for a digger when all you need is a shovel, if you need a latrine dug why pay thousands for a digger, when you can get a pleb with a shovel. Sure the pleb with the shovel might advance to the point of being a digger, but until that point why pay for it.
Also experienced devs might get bored with stuff that they consider menial where a recent grad can learn an awful lot form it.