Imagine if you went out and paid $40k for a super sweet TV, and then some friend comes over and tells you about his TV, which is actually better than yours and only cost $2k. You aren't going to believe him no matter what he says, because doing so is admitting that you did something very very stupid.
The same is true for higher education. At the undergrad level, outside of certain technical areas, the entire value of the degree is due to the belief that it is valuable. As long as more or less everyone continues to believe the degree itself has inherent value, it will continue to be valuable. Even if something obviously better and cheaper comes along, those that have bought the proverbial $40k TV are going to continue to insist it is better, for fear that admitting otherwise will make their degree worthless.