Differences in student load at liberal arts colleges vs. research universities
As with other commenters, I think the premise here is flawed.

I teach at a public liberal arts college which is typical of many. (Certainly our curriculum and requirements are in line with other schools in the COPLAC Council of Public Liberal Arts Colleges.)

Our students are required to complete 120 credits to graduate, which over four years averages to 15 credits a semester, or five 3-credit courses. I don't believe there is any serious difference in student course load when compared to large research universities (but maybe someone will prove me wrong).

The main distinction about teaching at a liberal arts college is that the overall curriculum is broader, and students do not focus on specialization as much as integration of diverse subject areas. Instead of taking 70 or 80 credits of (say) computer science, our students take only 40-45, with the other two-thirds of their degree consisting of courses in other areas. In this way, students build a broad, integrated perspective which incorporates their major into a study of the world at large. The focus at liberal arts colleges is to help students become better critical thinkers, decision makers, and problem solvers, rather than becoming subject matter experts in a narrow discipline.