"These were already signed off/approved/whatever".
"But... you ONLY did a wireframe of 3 screens, for iPhone 13 only, in portrait, and ... we already have to support desktop/tablet/mobile."
"Stop deviating - we already interviewed customers!"
"But... you don't actually show what should happen in various hover/transition states. You haven't accounted for multiple lines of text in these screens. You haven't accounted for different font sizes... etc"
"Stop deviating".
I've had a couple of good experiences working with a couple design folks in the last year, but EVEN in those cases, "design" was sort of treated like "one and done".
Once the product is in the hands of real users, feedback - implicit and explicit - comes in, and there should be processes in place to make rapid adjustments - possibly multiple iterations - to deal with the feedback.
That's one of the biggest hurdles I've seen, even when there's decent collaboration and respect.