Code:
https://movieweb.com/gi-joe-3-delayed-dwayne-johnsons-availability/
"G.I. Joe 3 Delayed Due to Dwayne Johnson's Packed Schedule...

You would be hard pressed to find a movie star move busy than Dwayne "The Rock" Johnson these days, but he honestly may be a little too busy. His inclusion in the G.I. Joe sequel G.I. Joe: Retaliation helped make that franchise a hit, but a presumed G.I. Joe 3 has been heavily delayed due to Johnson's packed schedule. At this point, it looks like it may be quite a while before we see the movie make any progress.
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He is also attached to star in Journey 3: From the Earth to the Moon, as well as playing Black Adam in the DC Comics-based Shazam!. Not to mention a sequel to San Andreas, Shane Black's upcoming Doc Savage adaptation and a supposed in-development remake of Big Trouble in Little China. Oh, and his HBO show Ballers has been renewed for a third season. So yeah, busy is a bit of an understatement, especially because many of the movies on this slate have sequel potential." ..!

A little bit more with the above link...