Note that I am an expert in this field, probably one of the top few thousand people in the world in networking: There is no technical reason at all to have data caps, only financial ones.
I know expertise doesn’t matter anymore, but there you go.
As a sort-of aside, data caps tend to actually increase network usage. Why? People who have a cap often feel they “have to get their money’s worth” and use the service right up to its limits. Just a human behavior thing. So that’s why most often data caps lead to more network usage, not less….