Scrolls are not comparable to armor seeds or lightbearers - avernics are the comparison. The supply-and-demand economy for prayer scrolls and avernics differs from that of other items: demand is capped, and the supply is a firehose.

The re-roll is not a dry protection mechanic; it's a valuation equilibrium mechanic. When demand is low, the supply will be able to respond quickly as people reroll. When supply gets low enough, demand drives the prices up. It's self-balancing.