I was surprised to see those too exchanges listed too.
Both Polo and Bittrex are in the crypto industry for so long already. Though some might find them not a good exchange to go to, but for me, I trust these 2 exchanges as compared to new ones.
The discussion here isn't about good exchanges, if it were we have many good ones out there. we're speakings of best of the best exchanges currently in the market. Tge two I highlighted from tge list, never said they were not good (cause they were) remember I indicated i once used them at some stages of my cryptocurrency journey. But when you're classifying exchanges, there are some current factors you consider, like; trading volumes and their impact on the grown of projects. Availability of more trading pairs etc. Poloniex and bittrex were onces at the top of the fruit chain but now they're closer to the button. We have exchanges like OKEX that wasn't mention when they're currently one of the best out there.