https://www.cbr.com/superman-arrowverse-solo-series-rumor-analysis/2/
If that solo show is given the green light, the release of a potential Superman series could seriously undermine the potential success of Batwoman, a hero that’s relatively obscure to mainstream audiences. Worse, Superman, as an iconic, popular superhero for the better part of a century, could cause the popularity of Supergirl — which itself had already built up the significance of Superman early on for obvious reasons — to quickly diminish.
It doesn’t make that much sense for The CW or Warner Bros. to introduce a Superman solo series, via the Elseworlds crossover or otherwise, when they’re already focusing on the introduction of Batwoman. The hero clearly needs a decent chance to be established in the eyes of television audiences, something even Supergirl needed time to do in earlier seasons.