Trailers are often put out without finished effects, and Rogue One is notorious for missing scenes and sequences only ever seen in promo materials. If there’s a “why” it’s probably just internal production troubles and budget. Some said get a trailer out by certain date, someone else say “good enough” to the unfinished shot.
There are a bunch of threads here already, plus one of our members made this site you can check all the many things that were chopped and changed: