No shit. Bitcoins cant be created from debt.  Unlike the fiat world, a growing bitcoin economy doesnt create more coins, only mining creates more coins at a fixed rate. Therefore its impossible to expect a % profit from investing your bitcoins, as for every coin you win someone else has to lose one. Where does the loss come from? Not from my cold wallet, thats for sure.

Bitcoin is a commodity, not unlike gold. How often have you seen an advertisement "Put your gold to work, earn x% per day for depositing gold with us" ?

Your investment is the bitcoins themselves.