These whales have been deciding since the December of last year not to increase the price and hence see the market that is just revolving around a specific amount. They can use their power to do anything.
Whales are good at what they do, but they don't completely rule the market as you think they do. They'll only start dumping when they think the time has come and there is no more room for further increases.
In case of last year it was pretty obvious that the market wouldn't make it past the $20,000 mark, which they used as an opportunity to liquidate their holdings. After that people went nuts and kept selling the market down.
Only in the last weeks before the push back to the $10,000 mark it was pretty obvious that whales were accumulating and artificially kept the price below a certain range, and when they were done, current levels are the result.
That obvious manipulation should have been used as an opportunity by non whales to do the exact same thing.