Bittrex to de-list cryptocurrencies

Bittrex have added only a few of the hundreds alt coins that have been released in the last 3-6 months, and for the past 3-4 months, no cryptos were de-listed from the exchange, but yesterday, October 3, 2017, out of the blue, the announced they will be delisting a few alt coins, including the following:

BTC-BTS
BTC-BTA
BTC-DAR
BTC- DRACO
ETH-BTS

Please note that these alt coins has only 10 days life/left on the Bittrex platform, thereafter they will be erased from the Bittrex platform (October 13, 2017). I want to make a note on Bitshares (BTS) in particular.

Let me draw a short analisys on BTS (Bitshares) https://bitshares.org/
Some facts:

Source: https://coinmarketcap.com/currencies/bitshares/#charts

BTS has been on the market since April 2013 and has over 155 million USD dollars market cap, and their daily trading volume is huge, always in the region of 10-13 million USD. What is even more interesting, according to records on www.coinmarketcap.com, BTS is listed in 60 different exchanges. BTS has a solid team of developers and has just released interesting projects they are working on. BTS also has a very active community and they are always providing updates on Steemit, Twitter, Reddit, etc. In fact, Bitshares just published on Twitter that Bittrex did not want comment or give them any specific reason for de-listing them.

Pertiment question: what is the real reason for Bittrex to de-list a solid alt coin in such a short notice?

I appreciate your comments and answers.