Sorry for late response...
I believe there would be multiple different reasons why some would choose to invest in HBD or not. It can be one of the reasons you mentioned or the combination of them. While it is not easy to tell, I think this can be a good research project.
However, I would guess those who have been on Hive for a long time would consider HP as a better investment option. The ability to increase influence in governance and rewards distribution with continuously growing HP on one hand might be more meaningful for those who use the network regularly, and also just a habit.
I personally had a habit of always converting HBD and Hive to HP. I haven't considered accumulating HBD in the past. For me it started when I came up with a list of items that I wanted to purchase with HBD, just as an experiment to demonstrate benefits of Hive network. Then inflation happened, witnesses started signaling higher APR, and it made sense to keep HBD in Savings. This too became a habit.
With this high APR, I think it can be beneficial to invest in both HP and HBD. I consider HBD as a hedge for Hive, and thinking about keeping 90% in HP and 10% as HBD. When Hive prices are high it is great, HBD is still there. When Hive prices drop lower, it gives an opportunity to buy more Hive and increase HP even higher.
It would be interesting to know the investment thought process of long time Hive Bees regarding HP and HBD.
Thank you for a great question!