There's also risk distribution: if you rent your hardware for 80% of the value, you're sure to get 80% of the value, while the risk is portioned up among many smaller investors, all of whom could reasonably stand a loss; if you don't, you're stuck holding the bag entirely if something goes wrong (eg, the has rate speeds up more than predicted).

There is a value in risk distribution that can cause mining hardware to be a good idea to rent out pieces of even if you're likely to make money on it, as long as the risk of losing money isn't trivially small.