Supply chain is hugely complex : from demand forecasting to supplier management to factory management to inventory management to logistics management. Every one of these "management" systems require its own software. These software often are "on-premise", which means it it hard to share globally, no mobile access, usually not real time, is hard to use, and does not integrate well with the other "management" systems.
To illustrate how separate "management" systems have to work together, here is a diagram:
