When people stake, even for 3 days, it takes those coins off the market. They can't be sold even if the price were to increase above $1. That removal from the volume of potential sellers should tend to increase the price a bit more than paying the same rate interest on fully-liquid HDB.
Since some people do want fully-liquid HDB, they would not receive interest and the total cost of interest would be lower and/or the rate of interest higher for those who do get it.
RE: Request for comments: HBD stabilization DHF proposal