Although many smart factories currently use a combination of 5G and Wi-Fi, the security and connectivity that 5G provides factories are seen as more advanced than Wi-Fi.
When smart factories choose 5G over Wi-Fi, they can get:
Encrypted traffic as it rides through the network
Seamless connectivity to transfer traffic between networks and keep sessions intact (a big challenge with using mobile technology)
No urgent upgrade requirements when switching to a 5G network