I don't think being astute has anything to do with it. Even now, book adaptations into movies, series, etc happen all the time. Even Disney still lets various

I don't think being astute has anything to do with it. Even now, book adaptations into movies, series, etc happen all the time. Even Disney still lets various companies (including freaking Warner Bros) make video games of its various IPs. The dynamic here isn't about being astute, it's about well-positioned for a given market. If Disney thought a Frozen show was a good idea, they'd produce it themselves (like they did for Tangled and various others). For markets where they don't have / don't want to have an internal talent pool (RIP LucasArts), they rent the license.