Initial is for sure more expensive.

I think this is a more valid reason than your recurrent one but.....

How much does it cost an airline to cancel a flight? 5k? 10k? I don't know the answer but I'm sure it's up there.

At some point doing initial for part time employees could simply be cheaper than canceling a bunch of flights every day.

Again, there is a point where this would make sense. Some bean counter just needs to come up with the number.