Eh, I don't think anyone participated because they just really wanted Netflix to have a better recommendation system. Teams put serious effort into it for the million dollar prize, which wasn't a lie. And hackers and tinkerers enjoyed the novelty of the challenge and the cool dataset to work with, also not a lie.

I don't think they ever said they would use it necessarily either? I feel like it was obvious that it wasn't going to capture all of their actual requirements - your algorithm could be slow or expensive or difficult to adapt to new requirements or difficult to adapt to new data etc etc.