He believes the current collective bargaining agreement played a major factor.
"Everybody is an expert out there on Hackenberg and thinks he can't play. It's unfortunate, this whole collective [bargaining agreement]. How do you develop a quarterback? I don't know how you do it.
"It is hard enough to get Connor Cook enough reps, let alone a fourth guy. It really depresses me how we can't spend more time with these young quarterbacks, and it is really going to be an impactful situation on the NFL in the future."
Oakland acquired Hackenberg from the New York Jets in late May in exchange for a conditional seventh-round pick. Despite being taken with the No. 51 overall pick in the 2016 NFL draft, he never saw the field for the Jets.
That turned out to be the case in Oakland as well. The team waived the third-year quarterback Tuesday.
It was reported last month that Hackenberg was revamping his throwing motion (quarterback guru Jeff Christensen said he had to "start from scratch," per NFL.com's Chris Wesseling) in hopes of getting his career on track. However, New York had re-signed journeyman Josh McCown and added Teddy Bridgewater in free agency and Sam Darnold in the draft.
The former Penn State passer became expendable as a result. But with Derek Carr solidified as the starter in Oakland and Connor Cook and EJ Manuel providing decent depth, Hackenberg faced an uphill battle of making the team, especially given the fact he changed his throwing motion.
"[Hackenberg] has been working on changing his stroke, his passing motion, and I think he did that," Gruden said, via Sando. "We just didn't have enough reps to take a good look at him. Since we were further along the road with some of our other guys, we didn't have the space."
Time—and the CBA—worked against Hackenberg.
ESPN.com's Field Yates reported on Thursday that Hackenberg had a visit with the New England Patriots scheduled. Now that Jacoby Brissett and Jimmy Garoppolo are gone, veteran Brian Hoyer and rookie Danny Etling are the only passers on the depth chart behind 40-year-old Tom Brady.