I wonder if it depends on how much he thinks he's developing at PSU
His freshman year under NFL guru O'Brien he did great. His sophomore year under Franklin he did not so great. Isn't freshman to sophomore year where you usually improve?
If his junior year is like his sophomore year then maybe you think he's not developing or not suited to the offense. Then maybe he goes pro, which sounds bad after two so-so college years, but the point might be that once you go pro you start getting NFL QB coaching and you develop. Maybe you get drafted lower after two so-so years but with the rookie wage scale the big money in the NFL as a QB comes from ending up being good, not from signing a big rookie contract (see Russel Wilson, a 3rd round pick in 2012 that is soon to sign a big contract). If you're not developing in college why stay another year?
If Hackenberg goes pro in 2016 and if Houston does well enough in 2015 that it looks like O'Brien is going to get to stick around and if Houston still isn't set at QB maybe Houston drafts Hackenberg and he's reunited with O'Brien.