I can't even remember when last I used bittrex as exchange again, unlike before there popularity has dropped drastically over the past years, I don't think this action will have such huge impact.
Binance has made it difficult for exchanges to compete with it. It is difficult to compare the security of the exchanges but transaction fee and easy of binance exchange has always been improved both for mobile app and website. All the 3 Coins to be delisted have quite a good volume of trade for any pair on the exchange, which is a pointer to SEC regulation. It could be a means to reduce coins in this market that had failed the regulation in the past.
well, the Binance exchange has indeed had a very good development and many are using the Binance platform because it is easy to use, the Binance exchange will only list coins that have clarity, when there is a problem like XRP then they will also take action to remove the coin from the list.