I would think that the conservatives that are qualified to teach in universities would probably rather make more money by applying their skills in the business world. 
To be a professor requires wanting to be one (usually).
I do not believe that any left bias is intentional (at least not in a conspirators way). You simply have schools that want to maximize their profits, so they offer more degree programs. They tend to be in areas that didn't used to have degree programs (i.e. Asian Studies), which themselves tend to attract both liberal profs and students. It's not a big, scary plot to brainwash youth, just a result of simple economics. Student loans are guaranteed to anyone that is admitted to a university--why turn them down? Create a degree program that appeals to previously untapped markets!