But the problem is that every captain ON THE AVERAGE needs to stick around at least 1000 hrs AS A CAPTAIN to mature THE AVERAGE FO to be upgrade eligible. Any CA leaving without sitting in the left seat long enough to season a replacement means a loss of 121 upgrade hours. For that matter, any FO leaving takes all those hours of seasoning with them and also hurts the regional. But ultimately, if enough CAs leave without providing enough time in the left seat to enable an FO the experience to upgrade, you get in a death spiral of not having enough pilots to fly the trips. You can stave that off awhile (look at some of the bonuses being offered for DECs, but as those DECs acquire more time they also become more likely to be recruited by a major. It’s a queuing problem. Survival of the airline is dependent on retaining enough CAs long enough to mature the next generation of CAs at replacement numbers. Kind of like COVID. Force the R0 under 1.000 and the virus will eventually die off.

If you don’t have a CA the flight doesn’t fly even if you have a dozen extra FOs.