hCaptcha is designed to solve the most labor intensive problem in machine learning: labeling massive amounts of data in a timely, affordable, and reliable way.
More data generally produces better results in training machine learning models. The recent success of deep models has led to increasingly large datasets, almost always with some human review. However, creating large human-reviewed datasets via Mechanical Turk, Figure Eight, etc. is both slow and expensive.
hCaptcha allows websites to make money serving this demand while blocking bots and other forms of abuse.