You don't submit an algorithm, you only submit your predictions. Your algorithm to generate your model predictions is not known to Numerai.

The data you work with from Nunerai is obfuscated, so you can't take it directly to the market.

It is an interesting no-risk way to evaluate models/algorithms. A lot of people are there to learn on a tough problem.

Edit: The reason for the coin is to allow data scientists to give confidence information about their models. There is an additional payout in USD associated with NMR staking (currently an extra ~$4000/mo for the most consistent models).