I think they were hoping to lean into the uncanny valley of AI art to cause a sense of imbalance/discomfort to fit the whole secret invasion theme. And of course save a boatload of money along the way.
I'm not necessarily against it as a concept 'cause I think art will survive AI as it survived digital painting, photography, and loads of other revolutions before. But it really is kind of a slap in the face to the artists that got Marvel where it is today.
It's reasonable to suspect that something like this might be important and denying him the truth is denying him agency to choose.
It may be the case that you would rather not know. How can you guarantee the same about another man you've never met?