You ALWAYS have a strong contingency at backup QB. Especially in contemporary football where the injury protocols keep players out for lengthy terms.
BTW? We also saw the exact reverse effects of what you are implying in the success of backup QBs who carried teams well into the playoffs. This isn’t a big secret. You never go in with blinders on and you always have a backup plan. That’s at any position too, but especially the QB position.
Now we can certainly argue about the resources or capital used to secure a contingency plan, but not one team in this league is thinking they don’t care about a backup QB or they’ll just call it a season if the #1 goes down. Conversely, they each are desperately trying to evaluate the best option at #2-#3 QB to position themselves to keep Winning. Furthermore, teams with great QBs are constantly attempting to draft the very best insurance they can and you see this around the league each draft. Remember too, Brady was a 6th round pick.. can you imagine had NE ignored that philosophy?
The Packers traded for Kizer, a 2nd. round pick that McCarthy characterized as a 1st. round talent. It's not for lack of trying. Even 1st. rounders suck as rookies and lose games. Veteran backups who look like they can win games are expensive and prefer to go where they can compete for the starting job in front of a rookie to get to the next contract.
Even if you think it is time for a succession plan, like New England drafting Goroppolo, even if he gets to the point where he can win a couple of games he's out the door before year 4 if the plan was premature and you're trying to recoup some of that draft value.
Cost and timing is tricky. Few teams highly reliant on a second contract (or beyond) franchise QB have some reliable winning solution. Most games are decided by 7 or fewer points. It doesn't take much fall off in QB backup performance to sink a contender to 8-8 or worse.
What you want is somewhere between very difficult and very costly.
While I couldn't agree with McCarthy's assessment of Kizer, I see improvement. You gotta figure it takes time to get 0-15 out of your system and back to some level of confidence. He might just do all right if called upon for a few games in the weaker part of the schedule if this is in fact a good football team. If it is not a good football team it is not going anywhere with Rodgers or without him.
Kizer's biggest challenge is 3 offensive schemes in 3 years.