Maybe some of the founders are hoping that XRP will become the currency of the future and hoard it - but that would mean killing their company by pricing transactions to high.
This seems to be nothing but speculation.
The stated monetization strategy for the Ripple system is to hold some XRP and hope they increase in value. The optimal execution of this strategy is to balance the opposing goals of wide adoption versus XRP price maintenance. It is against their economic best interests to price transactions too high.
The easiest way to stabilize transaction cost is to use the hoard of XRP to fix the price relative to another currency (e.g. Bitcoin).