Because in the industries I have experience in IT has typically very little to do with the type of efficiency that matters in manufacturing. For instance, moving a factory from Germany to Romania is going to give you faster and more predictable savings than, say, optimizing production with IT and automation (obviously take this example with a grain of salt and the usual "it depends").

The theory was that Industry 4.0 should somehow change that, at least in Europe, by adding more automation and tech to production. I have seen only 1 factory built that way and, let me say, it was a complete mess IT wise. There is also the issue that the same people that were building factories in the 90s are now also building the "new" factories.