Revealing mistake: When the Batcycle slams against the taupe BMW blocking the road, there is no driver inside, to allow for a safe stunt.
Revealing mistake: During the chase in Gotham, the armoured truck crashes against a jeep. The driver remains stiff as a board, unaffected by the violent impact or any laws of physics, revealing it's a dummy (or a CGI asset).
Revealing mistake: When the Barrys cross through the glass door, for a couple of shots, Young Barry's face is replaced with a non-realistic CGI face with features that don't match the face contour at all.
Answer: Some possible reasons gleaned from the Internet: Filmmakers wanted a different vision of Supergirl to reflect a darker, grittier personality and to show her refugee-like experience. Her dark short hair symbolizes her harsher journey from her home world. Also, it gives her a more androgynous look, reflecting both her feminine and masculine traits. Adopting a radically different look for an established character also shakes up viewers' expectations and generates more publicity and interest in the film.
raywest ★