Generally, teams like to take one quarterback per recruiting class to make sure there is plenty of depth on campus. That’s kind of where Purdue is right now. David Blough is the entrenched starter and likely will be through 2018. Elijah Sindelar is the backup getting pushed by Jared Sparks (who will probably play some receiver), while Nicholas Sipe and Griffin Alstott are incoming in the fall.
All that can change in a heartbeat with transfers and injuries, so getting a quarterback every year is a good idea. Today, Purdue got its 2018 quarterback in Jack Plummer, a 6’3” quarterback from Gilbert, Arizona.