Unfortunately lots of stuff gets optioned without being made. I'm pretty sure @scalzi.com once said he had something optioned because a studio had something similar in development, and wanted to prevent anyone from using his to make a competing film. I do know Terry Pratchett says he wouldn't...

... believe a Good Omens movie/series was actually happening until he was sitting in a theater with a bucket of popcorn actually watching it. But yeah, it's gotta be pretty shitty to be on the receiving end of a studio rug-pull. And sounds like it happens far too often.