Once upon a time — specifically, from the dawn of the “talkie” in the 1920s until just a few years ago — Hollywood’s calculus regarding how sequels got made was simple. A movie came out, did big business, won over fans, and the captains of industry in the studio C-suite called out for another one: the same again, only different. These days, however, the forces dictating which films get sequelized and which don’t has become a much weirder science.