I taught multiple courses each day, at least two and sometimes 4. I taught applied math, algebra, algebra II and pre-calculus at various times. In social studies I taught government, American history, World History, economics, law and justice, and life skills. I often taught social studies and math at the same time. In one school, I taught the exact same students math in the first year, and social studies in the second year. Teachers now usually teach in teams, meaning the same students are in each teacher's class, they move from one to the other. I was a team leader before I became an assistant principal where I had 4 teams of teachers.
Were you taught that way? That is why your education is atypical compared to now.