Exchanges aren't active members of the community on their accounts. They just have to use a steemit account to be able to transfer funds back and forth.
I think poloniex has a lot of history to buy assets from other exchanges to have them available for the demand their users if the time comes. They bought a lot of eth at one point too.
You have to remember though that everyone knows this is open-source and anyone van analyze and check for shady things, with this in mind you have to remember that if something fishy really is happening, it won't be this obvious and open to the public.
I moved most of my assets away from Poloniex when they implemented the changes to trading fees and basically made it cost nothing for whales that trade a lot and like to manipulate the market and I think that's what's happening now with so many altcoins having daily pump and dumps.
If you aren't profiting from it, someone else is and someone else is losing from it too. That's why I don't day-trade anymore and invest for tje long hauls instead.
Thank you for your comment. I think that my post is almost invisible and there is no many people who understand markets. I am pretty sure that some guy is doing triangular arbitrage right now between our internal market and poloniex. He has at least minimal fess or 0 . This was a reason why I brought this post.
I do trade a lot and I see market manipulation on daily basis. I am not happy when I see similar behavior at steem market as well.