All exchanges, even legitimate ones, offer discount packages on anyone who has high volume.
Ex: Interactive Brokers (a legitimate online exchange for stocks) hit it big with its monthly-subscription model: $$subscription / month $20 / for severely discounted trades (fractions of a penny per trade). https://www.interactivebrokers.com/en/index.php?f=1590&p=sto...
Yeah, I get it, but unlike stock transactions crypto exchanges generally take a % of volume traded unlike stock exchanges which take a per-transaction fee instead (I think options might be an exception where there's a per-contract fee..not sure).
If you're about to dump $10,000 to $100,000 worth of fees upon an exchange per month so that you can perform price manipulation (or whatever), you give the exchange a call.
They'll answer. You explain to them that you want to give them $50,000 / month (or something) for 10-million trades/month or whatever.
If they let you, you do it. If they don't, call up another exchange and give them the same offer.
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Its called business. When the $$$ amounts go up beyond a certain amount, you make it worth their while to treat you specially. They want the volume, you want the trades. Old-school business, just talk with them and things happen.
I kind if assumed it was the exchanges themselves faking it. Wash trading without colluding with the exchange is pretty expensive.