Why do operators choose nb-iot?

Because NBIOT can be modified on the basis of the communication base station itself, that is to say, the network can be built without too much workload. Then operators can master this data channel to charge and increase the number of access terminals. In short, it is beneficial to performance and political achievements.

As for the rest of the communication technology, the most typical one is LORA, which can be built by almost anyone, and has little relevance to operators, who are relatively uninterested.