IOWA CITY — Thousands of students who enrolled in one of Iowa’s public universities in the fall — despite the raging pandemic promising a vastly different collegiate experience — did not return for the spring semester, according to new campus census numbers made public Tuesday. The University of Iowa’s spring enrollment of 28,320 is down about 7 percent from the fall’s 30,448 count — which already was continuing the campus’ steady enrollment decline from a peak of 32,323 in fall 2017.