user3627: They have every motivation to do so. 
Extreme volatility is bad for confidence and can hurt the chance of Bitcoin becoming a respected currency.
Say for the sake of argument that Satoshi owns 500,000 BTC. This is a conservative estimate.
Someone holding that much BTC could easily dampen the wild price swings we are seeing at the moment by selling large quantities when the price spikes and buying them back when it crashes.
By doing this they risk losing a fraction of their bitcoins.  However, this would also increase the probability of bitcoin’s success and them becoming multimillionaires. 
Which would you choose? 

50% chance that you own 500,000 BTC worth $500 Million USD in 2017. 50% chance that bitcoin fails to take off and they are worth $5 Million USD.
80% chance that you own 300,000 BTC worth $300 Million USD in 2017. 20% chance that bitcoin fails to take off and they are worth $3 Million USD. Plus $16 Million USD profit right now.

Note: The above numbers are not meant to be scientific. They are just simplifications meant to illustrate the gist of my argument.
I don’t see how any rational person would choose option (1), unless they have some really crazy lopsided utility function for money.
So why isn’t it happening? Why are most coins mined in 2009 practically untouched?

user1409: There once was a guy named pirateat40 who had been trusted with a lot of Bitcoin. On August 17, 2012, he decided that he didn't like how quickly Bitcoin was gaining value and decided to sell a chunk of his holdings at a low price in order to bring down the value. He may have recovered his losses, if he did at all, by rebuying low and up the rise in price.

He claims to have done this several more times, but to a lesser degree.
Here is IRC transcript. I was in the room -- I think #bitcoin or #bitcoin-otc on Freenode -- at the time he announced his intentions. I found this forum thread linking to it.

user5401: Implicit in "stabilizing" the price is the assumption that you know what the price "should be". Maybe the people who own the lion's share of bitcoins don't believe that they know what the price "should be". If they believe that they don't know, then it stands to reason that they would not attempt to "stabilize" the currency, since doing so while being wrong about what the price "should be" will lead to a loss. Why not rather just do nothing if making either a profit or loss would be, a priori, equally likely?

user3634: I think the idea is to have a system that is not subject to manipulation. Highs and lows may be what I consider growing pains but will eventually diminish provided there is confidence that the system is a true free market system. This means free of manipulation. Let the free market reign and value will be real. Manipulate it and we basically have another ponzie scheme like we have now with the US dollar. 

3627: <p>They have every motivation to do so. </p>

<p>Extreme volatility is bad for confidence and can hurt the chance of Bitcoin becoming a respected currency.</p>

<p>Say for the sake of argument that Satoshi owns 500,000 BTC. This is a conservative estimate.</p>

<p>Someone holding that much BTC could easily dampen the wild price swings we are seeing at the moment by selling large quantities when the price spikes and buying them back when it crashes.</p>

<p>By doing this they risk losing a fraction of their bitcoins.  However, this would also increase the probability of bitcoin’s success and them becoming multimillionaires. </p>

<p>Which would you choose? </p>

<ol>
<li>50% chance that you own 500,000 BTC worth $500 Million USD in 2017. 50% chance that bitcoin fails to take off and they are worth $5 Million USD.</li>
<li>80% chance that you own 300,000 BTC worth $300 Million USD in 2017. 20% chance that bitcoin fails to take off and they are worth $3 Million USD. Plus $16 Million USD profit right now.</li>
</ol>

<p>Note: The above numbers are not meant to be scientific. They are just simplifications meant to illustrate the gist of my argument.</p>

<p>I don’t see how any rational person would choose option (1), unless they have some really crazy lopsided utility function for money.</p>

<p>So why isn’t it happening? Why are most coins mined in 2009 practically untouched?</p>
 1409: <p>There once was a guy named <a href="https://en.bitcoin.it/wiki/Pirateat40" rel="nofollow noreferrer">pirateat40</a> who had been trusted with a lot of Bitcoin. On August 17, 2012, he decided that he didn't like how quickly Bitcoin was gaining value and decided to sell a chunk of his holdings at a low price in order to bring down the value. He may have recovered his losses, if he did at all, by rebuying low and up the rise in price.</p>

<p><img src="https://i.stack.imgur.com/Y3tHj.png" alt="MtGox chart Aug 15-21"></p>

<p>He claims to have done this several more times, but to a lesser degree.</p>

<p><a href="http://pastebin.com/PthgrzDS" rel="nofollow noreferrer">Here is IRC transcript</a>. I was in the room -- I think #bitcoin or #bitcoin-otc on Freenode -- at the time he announced his intentions. I found this <a href="https://bitcointalk.org/index.php?topic=101378.0" rel="nofollow noreferrer">forum thread</a> linking to it.</p>
 5401: <p>Implicit in "stabilizing" the price is the assumption that you know what the price "should be". Maybe the people who own the lion's share of bitcoins don't believe that they know what the price "should be". If they believe that they don't know, then it stands to reason that they would not attempt to "stabilize" the currency, since doing so while being wrong about what the price "should be" will lead to a loss. Why not rather just do nothing if making either a profit or loss would be, a priori, equally likely?</p>
 3634: <p>I think the idea is to have a system that is not subject to manipulation. Highs and lows may be what I consider growing pains but will eventually diminish provided there is confidence that the system is a true free market system. This means free of manipulation. Let the free market reign and value will be real. Manipulate it and we basically have another ponzie scheme like we have now with the US dollar. </p>
