poloniex and bittrex are both silent for a long time 
What does it mean ? I do not understand your title and its content. Poloniex and Bittrex are old exchanges, and they went through the hype stage. Currently, other exchanges such as Binance, Okex, and Kucoin are the first choices of investors.No, poloniex and bittrex exchange still have the latest updates, and they still list some new coins at their exchanges. But bittrex are actively added new coins at their exchanges, and the volume is also good for now. Poloniex is not too often to add the new coin, but their market still active, and if you check, both exchanges have a good volume. I agree that Binance is the top exchanges, and they still manage their exchanges to serves their member better.
The altcoin season will come, you don't need to worry, and you should have the patience to wait for that time.