Reason Why.
Polo is not playing with the BCH. Literally costing them $1Ms per day in fees.
Also they froze the LTC wallets. Steemians always bitch about withdraws.
Loads of other wallets are 'in maintenance'.
The whitefish is a bit stinky!
Another reason is they might have deposited (your) BTC on Bittrex and Bitfinex to corner the market and make a killing.
I HAVE NO EVIDENCE ... but I have a strong opinion based on observation.
All this FUD started after last delisting. Few rich pumpers decided to take grudge to Poloniex since was transparent and did not alert them in advance to dump their shitcoins. Now we see similar posts as your almost daily. With zero reasonable reasons or proofs. All that happened in last 3 montsh from delisting was that Poloniex volume and users trippled and more.