Presumably the reward amount is random with a few people getting dramatically more than everyone else. As if you got an entry into a lottery as a reward.
And they select the winner of the 1BTC reward as an influencer with a lot of followers for a great get rich quick scheme advertising...
They did this strategy with stock, maybe they still do. You got a random share that could potentially be Microsoft or Apple or what not and you could earn more via successful referrals.
I ended up getting some random pharmaceutical company whose name eludes me but it hovered around $5 the entire time I had it. I think it peaked at 8-9 once even, it was quite exciting for a neophyte like I was then.