I guess the market is prepared to buy 100% of the btc for sale at $5.10ish but not pay a nickle more. Why is this? Does bitcoin posses some quality that makes it inherently stable?
That is an incorrect assumption.
Price is always dependent on volume. There are enough buyers and enough sellers that any trade which isn't an outlier to
current daily volume can be absorbed without any significant change in price.
That doesn't mean the market is willing to absorb an unlimited volume without more slippage. Try dropping $1M USD or 250K coins on to the market and I guarantee you the market will move. Not only will it move directly (you simply sucking up the supply or demand) others will jump in and attempt to capitalize on that momentum.
The "calm" is simply a metric of depth vs volume. Depth has grown faster than volume (likely as many chased "free profits"). Today it takes "more" to move the price compared to a year ago. Volume while it has grown, it hasn't grown by a comparable amount. If volume quadruple and depth didn't increase you would see volatility take off again.
