My personal hypothesis (which I haven't tested with data) is that, because HBD has low liquidity on the external markets, the folks you listed above are injecting a relatively small amount into buying HBD there to [1] pump up HBD to set up the arbitrage opportunity you mentioned and [2] also pump up HIVE (i.e. perhaps buying up a lot of HIVE just before the HBD pump, then slowly selling off the HIVE at elevated prices that are being sustained by the HBD stabilizer).
That's all just a hunch, but it is based on the the fact that while I was looking at the data on Coinmarketcap after the last spike in HBD, I saw a spike in HIVE that occurred shortly beforehand -- it looked strangely coordinated to me (look at both HBD and HIVE on 4/24 from 6p to 9p CDT).
Basicly playing the both markets ... might be true ... but for the both cases, they need people to come and buy after they did.
Yes, of course.
I just wonder if it might be some folks who have figured out that a small amount of fiat (relatively speaking) can move HBD a lot (due to generally low trading volumes) and that a high HBD dramatically affects the price of HIVE, especially on the internal markets (partly because of the way the HBD oracle is used for rewards distribution).
In other words, could someone who has a relatively large existing investment in HIVE be using the HBD external market to pump up the HIVE internal market, taking HIVE profits along the way, plus periodically buying more HIVE (low) just before each HBD pump?
Again, just a theory -- needs to be tested with data. Even if a coordinated pre-HBD-pump buy of HIVE is not a real thing, using the low-volume external HBD market to pump internal HIVE (and internal rewards?) seems plausible to me.
Everything you wrote above is possible and probably happening to some extent. Hive has its history with Steem before and the speculators use the same principles for the two tokens. Its the ones with liquid hive/hbd on exchanges that move the market.
Yes, one of the disadvantages (imho) of tokens with significant rewards for staking is that it greatly reduces liquidity, thus making price manipulations much easier.