The fee improves the health of the network, because it incentivizes siafund holders to do whatever they can to increase the amount of data being stored. So Nebu

The fee improves the health of the network, because it incentivizes siafund holders to do whatever they can to increase the amount of data being stored. So Nebulous Inc. (developer of Sia and the largest holder of siafunds) wants to make Sia scalable and easy to use; other siafund holders might develop third-party apps or simply buy ads for Sia. Disclosure: I co-founded Nebulous.