It's surprising and alarming as well because I feel there is something really big which is been planned as these accounts have been active after so many years and I am sure 2982 bitcoins might not change the market situation but these are the only address which you have notified and there might be hundreds of other address as well and these might belong to one organization which is involved in manipulating the market.
This is not strange. Why do you think it's manipulation? There can be many reasons for an old account to wake up.
I'll give you some:
The owner died and the family gained access to the money. The family may not care about bitcoin and just wants the money
The owner got sick and needs money for treatment.
The owner got sick and knows he/she doesn't have much time left so it's now or never.
The owner finally had enough of waiting.
The money is being moved from one address to another. Sometimes to segwit, sometimes to something else.
The owner got a better investment opportunity like a family company that is in need of money.