Too many people love Christopher Reeve, and they went into preproduction on this just as Reeve died. So they cast a guy that looks just like a young Reeve, and they are tying this into Superman 1 and 2. 3 years ago, or 3 years from now, they may have made different decisions.
This also won't be an immediate sequel. It's set in our time, and Superman has been missing since the end of Superman 2.