HBD APR has no correlation with posting rewards, they're two separate things. Any talk about posting reward has to be carefully discussed (the actual reward, not the author/curator split) since it would have a significant effect on Hive inflation.

We raised HBD APR when BTC was >$60k and Hive was >$1, financially it was to attract new members, compete with LUNA (look at how LUNA went, right?) and since market was booming, we were able to afford it.

Technically, with the increased debt ceiling, we can still afford it, but its an additional risk after all. Since HBD interest is not connected to overall Hive inflation (posting rewards, curation rewards, passive HP generation, DHF, witnesses etc.) it is simply money printed out of thin air.