simply because of lack of demand!
most of these altcoins you saw already had an alt/USDT pair but nobody ever used them so the market was just there with some open orders that never got filled and only took up (wasted) space in their database so they removed the market.
but sometimes they know there is no demand for such markets so they don't even bother adding them in first place.
you see people want to trade with their bitcoins because they want to make profit on their bitcoins and increase the amount that they have. they don't want to increase their "USDT"! because at the end of the day 1 USDT is either 1 USD or it has finally collapsed and died. but 1 BTC was worth $500 in 2016 and $1200 in 2017 and now $6000 in 2018 and will be a lot higher as we go forward.
You are right, but other coins are being developed and may take place of BTC in near future so BTC may start to lose its value. BTC is just another crypto (with some issues). So BTC may also start to collapse. As you see, BTC dominance is variable, so we may see some day BTC dominance is 1%. most of these altcoins you saw already had an alt/USDT pair but nobody ever used them so the market was just there with some open orders that never got filled and only took up (wasted) space in their database so they removed the market.
but sometimes they know there is no demand for such markets so they don't even bother adding them in first place.
you see people want to trade with their bitcoins because they want to make profit on their bitcoins and increase the amount that they have. they don't want to increase their "USDT"! because at the end of the day 1 USDT is either 1 USD or it has finally collapsed and died. but 1 BTC was worth $500 in 2016 and $1200 in 2017 and now $6000 in 2018 and will be a lot higher as we go forward.
