it seems like I did not quite understand why it makes sense to deposit BTC on bitcoinpyramid.
It doesn't make sense to. By doing it you give your coins to the sorts of idiots that enabled people like Pirate, the people who think that high yield investment products are a great thing. There are some other questionable investments like mining bonds where in the best case you get a fixed amount of a rapidly depreciating asset.
If you want to gamble, actually gamble. Try out BitBet.us, BitZino, SealswithClubs, or even SatoshiDice. BitBet.us is pretty new, but I like gambling on outside events more than I like games of chance. There's also a number of fuller bitcoin sports betting books you can find on the gambling forums.