“@sharkbites That depends, it’s ~500 students or 14% of the class at USC. Students have the option of starting their college experience abroad. They say their Spring average GPA is 3.75, compared to the 3.83~ Fall average.”
There’s multiple reasons school’s do this, but mostly it is just good business. Keep as many seats full as you can for the highest average net tuition revenue. The rankings effect is certainly part of it, since having higher USNWR rankings leads to more demand for a seat in the school.
Notice that many schools that do size-able spring admits also tend to do a lot of transfers. USC enrolls 3,400 fall frosh each year who are fully on the books for ranking purposes. But then graduates 5,700 undergrads each spring. Like spring admits, it is easier to get admitted as a transfer than as a fall frosh. And transfers tend to be more likely to be full pays. Growing the class is baked into the model.
Since USC is in CA, their class size numbers would also reflect the CA tradition of kids moving up from CCs and lower tier Cal State schools. But you see the same pattern of growing the class size at a lot of the peer schools.