Interestingly that isn’t actually the case. I would guess most data used in ML is not human labeled specifically because it is so expensive and error prone. For example, most work done in the natural sciences simply utilize sensor data. Want to forecast some aspect of the weather? Grab a couple decades of historical data collected by weather sensors. None of that needs to be human labeled, only sensor collected. Some applications certainly do rely on manually human labeled data but not all, and I would personally guess only a minority of applications because of the difficulty in collection.