Asking Curry to come in on maybe a weeks notice to call plays was not likely to lead to good results for Curry or the team since he has never called plays before other than some preseason and the Senior Bowl. It worked for Brady in Buffalo, but Brady had play calling experience that Curry doesn't have.
So, going to Curry while the playoffs were still in play would have been a really risky thing to do and, as it turned out sticking with Carmichael was the right thing to do given what he did in those last 5 or 6 games since the offense really turned it around.
I too wanted them to give Curry a shot right around mid-season. Mostly because I didn't think they were going anywhere anyway and it was worth a risk to see what Curry could do. I'm just saying that this is the reason why the Saints decided not to give Curry the play calling duties. I, and likely you, were looking at next year and the future, but the team and DA were still trying to make the playoffs this year. And as it turns out, they were right because Pete did a good job as the play caller and likely better than Curry could have done with little to no time to prepare.
If, and I hope it doesn't come to that, Curry is hired as the OC he will have the offseason to prepare including 3 preseason games to work on his play calling. It would have been great to get him 6 games of experience at the end of this year, but I get why that is not the way the Saints went.