The “lower class” gap years are typically not planned gap years, or emergency gap years after being shut out of colleges that one applies to. More typically, they are due to the high school graduate not being immediately interested in going to college, and/or having a high school record obviously too poor to go to a four year college. It is only after work or military service that the person becomes interested in college (perhaps because then s/he sees that high school graduate work or enlisted military service is not that attractive a long term career for him/her) and gains the maturity to commit to college (often starting at community college).
This is quite different from the “upper class” gap years that are either planned enrichment activities, or emergency measures after being shut out and not wanting to start at a community college or less selective college.