From WBs point-of-view, what are the reasons to impose a (partial) Superman embargo on
Supergirl?
One possibility: It confuses audiences to have two live-action versions of Superman at once (Henry Cavill in the movies, some hypothetical actor in
Supergirl).
Okay,
maybe
to a
small extent. But I dont put a lot of stock in this concern.
Alternatively/related: With Cavill as the current and only live-action representation of Supes, it damages the movies brand to add additional iterations. How so? Well, casting Supes is notoriously difficult - or, at least, controversial. What if the new actor doesnt sufficiently look the part (in the face, in the physique, etc.)? What if his performance is lacking? What if the characterization/interpretation is conspicuously different from Cavills? Or what if the costume/muscle suit (on a TV budget) is noticeably inferior/cheap compared to the movie design? And what if
Supergirl happens to suck and/or is cancelled? (Maybe such a failure wouldnt tarnish Superman, per se. But it wouldnt be an
ideal scenario.) Finally (though perhaps implausibly ), what if the new actor and his representation of Superman actually outshone Cavill?
These strike me as more legitimate issues/risks - vis-à-vis WB being protective of the Superman image.