I wish the movie itself was in that expanded ratio. I wonder if they cropped it to 2.39:1.
Anyway, I think it ultimately comes down to the fact that 2.4:1 is a standard AR while 2.61:1 isn’t. Probably also to match with the other Star Wars movies.
But why bother to use the lenses used on Ben-Hur if you’re just going to crop it in the end? What was gained?