Kodak has an amazing automated film factory that can make huge quantities of any film really fast. Problem is that it's got a big fixed cost, and they aren't making huge quantities of film anymore. There's a big startup cost to make a run of a particular emulsion. Plus-X sold so slowly that they couldn't sell a minimum sized run before it expired. So it got discontinued.
This same factory also makes the Eastman movie films. Which are often manufactured to order. But shooting up one movie uses enough film that the order is a sensible sized production run!