I think the right sees a liberal bias among students and incorrectly concludes the colleges and universities must be to blame. I think it's more likely though that kids at that age and going through that process are full of hope. The act of getting a degree is driven by hope for a new and better future, and hope is the foundation of the left so kids will naturally gravitate toward a liberal bias.
This is admittedly a supposition on my part, but having sat through college courses where very conservative students tried to push their uneducated mentality that was clearly factually wrong and faced pushback from lecturers or professors with actual research behind their instruction, the act of education itself takes a student out of uneducated provinciality and gives them a more complete view. Someone that's uneducated is usually pretty provincial in their attitude and thinking, and if they perceive even learning about the wider world as change, they will attribute that to liberalism same as if a new attitude were brought into their little provincial area, even if it's merely giving them a more complete picture of what's wider than their scope of influence and experience.
The problem is that this is an outright reactionary approach, actively hostile to anything that requires the individual to do more than continue doing the exact same thing that has always been done. It's also foolish because it makes the individual less adaptable when other situations come along that require rolling with the change because it's happening whether or not it's wanted.
The little secret that people who insist on enforcing what they consider to be conservative values fail to get is that even in a society that is generally more permissive in a liberal sense than they want, generally nothing is stopping them from making the choice to live personally conservatively. One can even have incredibly liberal views and can still personally choose to live in a way that a conservative would find to be pretty normal and acceptable.