Because they entertain, making them primarily entertainers. We should reserve labels like "creators" for people who are actually building things, not streaming their lives on camera for an audience.
Semantics. If your bar for calling someone a "creator" is that low, then nearly everyone is a creator in what they do. But we have different classifications because applying one label to most of the population is not very useful.
Maybe this is pessimism, but calling streamers "creators" feels like a perverse label.