For many (most) traditional four-year college students, the primary value of the experience is something that a MOOC or Khan or whatever online can never ever replicate.
College is for many kids the first time you will live away from home, with all the distractions and temptations of the real world - but without losing your job and ending up homeless if you get too drunk and are too hung over to go to class the next day. It is a concentrated social mixing bowl where members of the opposite (or same as it may be) sexes come together with no parental supervision and have to figure out how to deal with each other - but also surrounded by a throng of peers to help them figure it out or support them as necessary. It is a halfway transition period between full-time schooling in which you are expected to learn and recite facts obediently and a world where you are expected to challenge authority figures and be fully responsible for all your own decisions.
It is, in short, the real world but with "training wheels" on.
I can't speak for anyone else, but four years of training wheels after high school just barely got me to the point of being a functional adult who didn't melt down when exposed to reality. (I also really, really, enjoyed it too.) Away from home, full-time, co-educational college is an experience at that period of life that I think is irreplaceable and can't ever be matched by a different model.