~Are there private individuals who own and posses such amount of Bitcoin? Yes, and it's easy to check just check on the blockchain, you can check each adress which belong to individual or company
~Why will one posses such amount as an Individual? whale basicly those that trust btc and gamble all in from beggining of btc. i know people that sell all their belonging to buy btc at 2011 guess how much they have now. they only sell 1-2 btc to hold on bank. 
~Are there any consequences to this? ofc they control the market, just like in stock or forex whale/institute exist that move and profit the most on the market, as we chase them to eat their crumb