You can convert HBD to Hive, but then you want to exchange the Hive back to HBD because that's how you store your wealth. The HBD to Hive conversion has no fees, but the Hive to HBD conversion has a 5% fee. So a bunch of people would be stuck with a bunch of Hive that they want to sell for HBD asap, which translates to big slippage.
You can convert HBD to Hive, but then you want to exchange the Hive back to HBD because that's how you store your wealth. The HBD to Hive conversion has no fees, but the Hive to HBD conversion has a 5% fee. So a bunch of people would be stuck with a bunch of Hive that they want to sell for HBD asap, which translates to big slippage.