It's either a strange decision, or we have to believe that up until the very point that Fran reopened the QB competition that Carney had shown more, and had more investment in practice priority in the program up until then, at which point Filardi suddenly overtook him and appeared to realize his potential at just the right time.
It's not great admitting it but it's much more likely the staff made a stupid decision than to believe Filardi's development timeline relative to Carney's happened to shake out the way it did. On a short week, at that.
My new conspiracy theory is that Nixon was never on board with the kind of QB Carney is, but it wasn't supposed to matter because Nixon was going to move on after this season when his son is done, and the likelihood of having to dip down to QB3 seemed so low at the start of the season.