Where are you finding these under center QBs in the college game? The college game is almost exclusively shotgun. It's not just the QBs being drafted, it's the college game period and honestly in recent decades the college game has been driving the NFL game more so than vice versa. Shotgun used to be a small percentage of NFL snaps, basically just obvious passing downs and stuff like the read option, RPOs, "mobile" QBs, etc. were just scoffed at by the NFL. All of these things are staples of a modern NFL offense.