Yes, but not everyone gets into the college recruiting gravy train. You either didn't go at a target school, or you didn't make the cut. Then you graduate and you're basically hung out to dry unless you know someone. This applies to many areas besides software engineering.

I mostly remember college careers fairs as a place where big companies tried to get you to apply for their internships.

Microsoft and Google and such usually had their own separate events, and I'll grant they were more serious about hiring people, though they mostly seemed to hire people who'd already been their interns.

Because the newbies will work for less. They will work longer hours (to learn the ropes.) They don't have families and health issues, so they are cheaper to employ as well. They are less aware of their rights and have less long term outlook, which would steer them away from these sorts of HR miasmas.

Thus they are just the filler needed by BigCo to compensate from the continuous braindrain. Once they have the skills and know the ropes, they'll either get promoted or leave for an employer of choice.