This may seem a bit odd to you, but it is not for much of the world's population, where a young adult is expected to help out the family as a whole with any income they may earn. For most families the decision on whether or not to continue their children's education is not taken for granted. But your family sees their standard of living decline, not just because of the cost of tuition, but also because you aren't contributing to the upkeep of the family. Note that in our calculations we did not let you work summers to offset college costs. Hence we could reduce our total by 4 times such earnings .
Personal circumstances vary widely.
The families of students on full scholarship face very different opportunity costs. Individuals with a trust fund provided by a grandparent may be able to draw down funds only for education. But for most of your families, college is a major expense. Your upkeep must be provided in any case. Society makes the decision.