Why should he commit to a full rebuild? There is no data that commiting to a full rebuild has a better chance of getting yourself into contention for a SB than staying in the middle of the pack. In fact it's more likely that you pull yourself out of the middle of the pack to become SB contenders ( See Chiefs , Eagles)
Luck is more a factor that committing to a rebuild( See Bengals and Wash) or even having a good QB that another team wants to trade for (See Texans, Lions)
No team just says the " the heck with it" we ars so bad at almost every position that we;re just going to cut or trade what decent players we have for picks and cap$ and just start over. No coach would ever want to stay or even the players you want to get would want to go there.
To do something like that you would have to have a crystal ball to know which QB in the draft would be the next great one AND when they would be in the draft. Plus you'd have to know who the next great HC would be because the one you have now is obviously not THE one
I think it's best to do what we are doing. Stay within at least a striking distance of being a contender , while signing young under 30 promising FAs . Having a good , because that what Carr is , good a bit above average and could be very good with help, as your bridge QB . Then hit, not even 2017 type hit in the draft for a couple yrs. And when your TEAM is gelling with the young players you get your QB . Even if you have to trade up to get him