Their main priority is to book as much profit as possible, and all that in a very short time. If the price falls back to far lower levels, then they will act by buying back the coins they sold.
No matter how much I love the increases that we have seen lately, if we from an unbiased perspective look at current levels, there is not much needed to see that the market is overbought.
Realistic prices for what we have achieved so far would be anything close to the $3000 mark. If we didn't had an upcoming hard fork to worry about this year, current levels would be well justified.