They will never do this, because it isn't in their interest. Doing so would undermine their brand; if people can pass the exams without taking the courses and paying tuition, how can they justify the high cost of tuition? Degrees are valuable if they are exclusive.
If universities were serious about social mobility, they would record and publicize the lectures.
Some universities publicize some of the lectures, but most lectures aren't publicized.
Again, this will never change, because it isn't in their interest. (Conversely, many lectures are publicized, because the value of a university to its students lies primarily in the exclusivity of the degrees it awards, not the knowledge it confers.)
I guess all this is obvious, but if it's obvious, why isn't it discussed? Why aren't there OpEds pressuring universities into opening up their programs, as I outlined above?