Its' because there are no trading fees on those specific exchanges.
Which means you can buy and sell to yourself at no cost.
This happens on "our" markets as well (the buying and selling to oneself) but fees make this prohibitive. On those specific exchange you are referring to, there are no disencentive to manipulate prices that way, hence the probability that a big % of this volume is "washed" as we say.
This is why such volumes are not taken into account.
Sonds legit. Altough the volume is huge, it would be good to find some mechanism to include it in the fee + current price.
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