Because Siacoins are not an investment. To me the supply model doesn't make any sense if you are concerned about the price per Siacoin. If hosts set the price of storage, and Sia is divisible, why design a coin that increases so exponentially? You could have 21 Mil Siacoins and storage would cost just fractions of a Siacoin. People have no incentive to hold Siacoins right now. Why would I pay for Siacoins right now when the supply will increase 4x in the next year. If anything, people are overpaying for Siacoins right now. Siafunds are the investment, because you are collecting Siacoins by doing nothing. Or am I wrong here?
At this moment, Siacoins and Siafunds can both be investment. Siacoins holders hold siacons and siafunds holders holde siacoin futures. They both are betting on same stuff. If Sia takes off and gets tons of users in the future they both win. If not, the both lose.
Edit - I forgot to mention the real winners will be the users and those who build business on top of the Sia platform.