South Dakota State does charge by credit, and the high tuition years/semesters correspond to high credits (e.g. 18 credits in both sophomore semesters for EE). It also looks like there are lab surcharges.
Starting at CC can save money to allow for a higher budget for a four year school the last two years. For example, if the budget is $80,000 total, then two years of a $10,000 community college (including commuting costs and food/utilities for the student at home) plus two years of $30,000 at a four year school would be within that budget.
It is true that students living in states like PA and IL do not have as affordable in-state public options compared to those in some other states.