I dont think scheduling has a lot to do with it, if they want to find a place for this they could have squeezed this in. More important than schedule, I think is money to make a show. All these project require money to make, so why they cant pick everything that gets a pilot or every idea that get thrown to them. And many other factors, obviously im not privy to all them, like BTS stuff.
Well when you got other options, as CW does with multiple pilots a year, I think all tiny factors, details start to count. What gets picked is not just about the quality of that project, but also how they feel it fares against its competition. CW is a small network, their numbers of pick ups is far low than other networks. The network is already oversaturated with 6 superhero shows, then they add on Superman and Lois, do they want to pick two superhero shows... I think its start to matter when you have to a limited 3-4 shows annually. They likely want different genre shows and there is also the WB-CBS split that has to be honored. Dont think Berlanti care much that there is gonna be a "clash" with his projects, he seems to just enjoy throwing darts at the wall. He threw in Kung Fu too, knowing CW had to chose between projects. Creating concepts and projects seem to be a sport to him. Whatever show gets picked up, he will get his salary either way lol.
I dont think its just one reason, I think its a multitude of issues and factors they weighed in. They went with and prioritised the competition [Superman and Lois, Kung Fu,,,], to me that says what they wanted and value the most . What they saw to be the better, more valuable projects for them...right or wrong.
Yeah maybe this spin off isnt dead, but it sure is hanging on by a hair's width.