Okay let's say there's sensors in the tips of the game balls.
The ball crosses the goal line. Is it a touchdown? I mean the sensors show that it crossed the line, but that doesn't really answer anything. Was it in the air? Was it a kickoff? Was it a pass? Did the receiver have possession? Was it a runner? Was he fumbling before it crossed the plane? Did someone step out of bounds first? Did they complete the process of a catch? Where was it when their knee touched down? A sensor doesn't answer any of those contextual questions. A really high tech sensor would possibly answer a few of them with decent accuracy.