The amount differs depending on the market situation within a particular year. For example, the market price of cryptos are high at the year 2017, the profit earned by many investors and users are high. But when the decline occurred after that, the situation reflected to the profit being earned by the users, as simple as that. It would be hard to determine the average income per year if the gap is huge, thus making the average income not accurate.

Also, no one would reveal the exact amount of their earnings for some personal reasons. But to give you an idea, just like what I have said, there will be times that profit will be big, and times wherein it would be low. I think this would settle the concern.