Because of sensor readout speed. Phones do what they do by shooting dozens or hundreds of very fast frames, then combining them into the finished picture. Came

Because of sensor readout speed. Phones do what they do by shooting dozens or hundreds of very fast frames, then combining them into the finished picture. Cameras can't do that, because their bigger sensors take longer to read out. There'd be too few frames, and too much gap between frames. Big sensors are slowly getting faster, too, with stacked sensors and the like. But they're not quite fast enough yet for phone-style computational shenanigans.