They use alt/BTC pairs and there are very few coins with alt/USDT pairs, so in order to trade a coin, we need to always have BTC, but BTC itself has huge fluctuations and at the end of the day we don't know where it's going to be stabilized, especially if we are investing for relatively short time.
There are certainly altcoin/USDT pairs in some exchanges, if not all. At least, I am using Bittrex, Binance and Kucoin and I can definitely say those pairs are available. However, we all know even with all that, the market is still in a way tied to bitcoin which is why we get to see much ALT-BTC pairs than ALT-USDT pairs. Things might change in the long run as more altcoins are being paired with fiat, but for now, it is not like it is not happening at all with the way you painted it.
It's a symptom of a young market, and it will persist until we get those fiat trading pairs.
Yes, as far as I am concerned, most of the reputable exchanges that I know do have Altcoin USDT pairs even though it may not be applicable for every coin in the market but there are substantial amount of good altcoin projects that is being paired to fiat for trading purposes. They may not be as much as btc pair since we know beforehand, everything was basically tied to bitcoin but it is a start and we are going to get to see more of it in the long run which should be able to make most of the alts stand on their own.
