Digital photography ISO measurement, why uniform across whole image?

ISO is been around since analogue photo times. Any, it should have been uniform for obvious reasons - you could never know what will be captured in each part of the film. So, you go uniform (ISO 100, ISO 200), select appropriate one for given conditions and do your best. Fast forward to today and we have same approach. Despite the fact that in digital photography "you know" or, rather, image sensor knows what will be captured by each pixel or group of pixels. Here's the question, why it couldn't measure sensitivity per area or, even, per pixel and have nonuniform ISO settings across the sensor? What prohibits having ISO level automatically set per pixel?