Best guess: “out for delivery” means “loaded into the van”. Especially if the projected delivery time is rather late, that is, you’re at the tail end of their round, it can happen that they won’t make it. And because FedEx isn’t being smart about things and flips route directions every day it can be that they won’t make it the next day, either, because you’re still at the end of the route. Only when your location is covered by another driver which doesn’t have you towards the very end then is the package delivered.

There’s various ways to alleviate that, in particular switching around routes so the tail end problem doesn’t hit the same people all the time, but I guess the penny-pincher MBAs that be at FedEx don’t see it contributing to the quarterly results. Here in Germany it’s usually along the lines of “we’re fucking busy, sucks to be you, we brought it to a parcel pick up, go there, next delivery attempt in three days, then it’s going to stay at the pickup until you pick it up or we send it back. Did you know that you can register with parcel pickup and have all your packages sent there also it’s self-serve. Please, it’s right next to the supermarket our backs hurt. Do something for the environment, :)!”.