With 2G and 3G, you could buy little modules that had cellular connectivity and could run basic applications - a lot of older smart meters did this using the cellular network. Sorta like how the ESP32 has a complete network stack inside it so it can do WiFi applications out of the box. But these modules don't exist for 4G and up because those networks are solidly IP based and have no room in them for legacy stuff, like voice, lightweight reporting etc. You want to do those, your application must talk IP.
Plus, for many industrial applications, it's easier to embed Linux.
Several companies are now offering new integrated chipsets with basic processing, RAM, cellular modem (2G,LTE, 5G ready) and embedded SIM (eSIM). One example is SONY semiconductor (Altair).
Doubt isn't the opposite of faith; it is an element of faith. - Paul Tillich, German theologian and historian