I don't know the exact numbers but it is consistent with other stuff I heard (notably the Brett Easton Ellis podcast which I recommend). Script writers churn a lot of scripts, many of them get bought but never produced. Or sit as a project for 10 years or more. But I think development doesn't mean they engage massive costs, just that they start trying to get the financing, perhaps with a tentative director and/or actor name attached to the project.
Yeah, there's a bunch of reasons Hollywood is notoriously known for "Development Hell" as its longest phase in the creative process. Production is generally "quick" and has a lot known knowns. Development is a lot of gossip and paperwork and contracts and writes and rewrites and license agreements and market studies and so forth, sometimes "forever" even for projects "everyone" thinks should be an easy thing to kick off and wants to see on some screen.
