"throw their receivers open", meaning that they throw it to where the receiver is supposed to be and it's the receivers job to be there and make the catch. If the receiver has run a good route and gotten separation, there should be little risk of the pass being knocked down or intercepted. But it appears that our receivers (except Lovett) aren't getting separation and/or the timing between Cook and his intended target is off or he (Cook) simply overthrows or underthrows it. Whatever the case, if we had a more consistent passing attack, I think you would see more big runs by our backs, i.e. passing to set up the run.
Maybe we're all expecting too much from Cook, in that he's only started a handful of college games. But I'm not sure he's the long-term answer, as we've all seen true freshman QBs on some teams come in and excel from the get-go (such as Johnny Manziel, Colt McCoy, Sam Bradford, Matt Barkley, Jameis Winston, Jalen Hurts, Jake Fromm, Trevor Lawrence and others).
Interesting SI article on home states of Top 100 college QBs:
https://www.si.com/college/2021/09/20/ncaa-football-top-100-quarterbacks-by-state