Every player develops and learns at different speeds. We hear this a lot, and we should know it. But likewise, some positions have steeper learning curves than others—something we also tend to intuitively understand. It’s a lot easier to play right away at running back than it is to play the quarterback position at a high level.
The cornerback position is one of the more complex spots on the field, so bringing in a member of the secondary at the last moment is tricky. You can find success, like the Pittsburgh Steelers did with Minkah Fitzpatrick in 2019, but not everybody is Minkah Fitzpatrick.