If form didn't come into it, I reckon he would play Giroud because he sees the tippy tappyness he brings with the lay offs and thinks that's what his striker should be doing.
All this chopping and changing helps no one, I still have no idea why Sanchez was removed from the role after his blistering start to the season. Theo should be the alternative if for whatever reason Sanchez is not central. The penny will never drop for him, dinosaur of a manager and one of the reasons he needs to go.
I like Welbeck but I know he's never going to be productive striker, he's just not switched on enough. Supreme athlete but only someone to use sparingly and for specific roles. Fergie always used to deploy him to do a job because that's how you get the most out of him, he never relied on him for goals.