The fork is set to reduce difficulty - therefore a rapid increase in the supply of coins - as you know, any rapid increase in supply is never good for price. Also long term, Sia has an impressive 3292.83 TB of network storage available, but only 114.49 TB is being used. That's a usage rate of only 3.4% - it is essential that this number starts to increase otherwise, the Sia project will likely fail - having over 95% of your assets idle is not good for any business, and isn't good for people holding the coin since nobody wants to buy it to use for storage (again supply and demand)