A ton of them his second year to make up for the McD years when players were transferring out left and right, then 1-2 since.
Since that first year lots of programs have taken as many or more transfers as ISU, heck Iowa's probably offered as many transfers and jucos since then. The reason ISU sticks out even after that big class of transfers is that ours are very high impact players generally.
McKay is technically a transfer but this will be his first basketball since playing JUCO. The big misconception is that players come here when they are in trouble. Clyburn came here because Utah sucked at the time. Chris Babb came here because Penn State sucked. Lots of the players are model citizens/students/teamates and they transfer because they see the program they are at is going down the tubes like the Lickliter/McDermott years were here.