So what were these “creative differences”? A rumor surfaced on reddit claiming that production was running behind schedule, but that doesn’t make sense given that filming isn’t even set to begin until July. The folks over at Latino Review, however, have a much more plausible explanation for the exit, as they claim that the script for Ant-Man—which Wright has been fine-tuning with co-writer Joe Cornish for many, many years now—went through a significant rewrite by Marvel that the filmmaker was uncomfortable filming:
About 3 months ago, Marvel had notes. The meat of the notes were about the core morality of the piece, must include franchise characters. etc., These notes came from the big four at Marvel. Joe Cornish and Edgar Wright did two drafts to try and answer the notes without compromising their vision.
6 weeks ago Marvel took the script off them and gave the writing assignment to two very low credit writers. One of the writers was from Marvel’s in house writing team. Edgar stayed cool, agreed to stay on the project, and read the draft.
The script came in this week and was completely undone. Poorer, homogenized, and not Edgar’s vision. Edgar met with Marvel on Friday to formally exit and the announcement went out directly after.
Read more at Rumor: Why Edgar Wright Left ANT-MAN