Off the top of my head, Matt Stafford, Andrew Luck and Trevor Lawrence were universally considered #1 overall pick basically from when they were in high school, yet the first year they were draft eligible they chose to go back to school anyway. Matt Leinart, Jake Locker, Sam Bradford, Justin Herbert, Marcus Mariota. There are tons of examples of players turning down the draft even though they are widely expected to be very high picks. Add to the equation that Sorsby had five million reasons to stay in college.
He certainly needs work in some areas, but it is a mistake to think that his projected draft slot must have convinced him to go back to college. He would likely have been drafted somewhere in the first round.
Also, I think you need to consider him with a day two-pick, if you are Ossenfort. Beck is surely the better scheme fit, but Sorsby has much more potential (and it’s not like he’s a bad fit). With all the “if’s” taking into consideration, Sorsby probably gives Ossenfort a better chance to save his job than Beck.