I'm sure this is happening gradually over time. I used to see whales dumping 1K-2K BTC at a time, several times daily, on Gox back in 2013. You never see that kind of volume anymore.
These were the good times. I remember seeing Chinese exchanges do crazy shit back in their +1 million BTC daily volumes. Orders of 10,000BTC were absorbed as if they were pocket change.
I think the main reason we don't see these dumps anymore, or much less frequently, is because of how investors are afraid of exchanges freezing their funds for whatever nonsensical reason. Right now they dump a few hundred BTC on exchange A, few hundred on exchange B, and so forth. It's a smart way to deal with the risk they expose themselves to, because the times of freedom are long gone.
The question is, how much of those volumes was fake? We know some exchanges faked their transaction volumes to attract people to their exchange.
This was also one of the reasons why some of these exchanges had to close their doors for a while, when their government sent inspectors to identify these practices
Today's volumes are likely no less fake
But that's mostly irrelevant as in 2013 prices had been way lower than they are now (I mean most of 2013, obviously), and dumping 10k bitcoins was not a big deal either specifically because it wasn't a huge amount in dollar terms. Besides, even if we crash to those figures (say, below 1k), we are not going to see such orders again for the simple reason that people are now very well aware of the true potential of Bitcoin as everyone has already seen it in action (read, no milk for exchanges this time)
. Like serious how can someone is saying that they need proof to show that there are something like whales who manipulate the market… lolzzzz. Which other proof do you need?? The things that are happening in the market should already show you that there are people who manipulate this market. Funny. 
