Selling your own NFT to your self for a profit, that's something else, but its not a wash trade as in that case there is a price change.
Lets say rich person X wants to conduct large-scale wash-trades to artificially increase (or decrease) the price of [insert cryptocoin here].
By conducting it on Exchange-Foobar, Foobar's traffic goes up, while rich person X gets the price change they want. Win-win for both parties.
EDIT: Remember: exchanges win on volume. They want more trades, they don't care if the value goes up or down.
I kind if assumed it was the exchanges themselves faking it. Wash trading without colluding with the exchange is pretty expensive.
Ex: Interactive Brokers (a legitimate online exchange for stocks) hit it big with its monthly-subscription model: $$subscription / month $20 / for severely discounted trades (fractions of a penny per trade). https://www.interactivebrokers.com/en/index.php?f=1590&p=sto...
They'll answer. You explain to them that you want to give them $50,000 / month (or something) for 10-million trades/month or whatever.
If they let you, you do it. If they don't, call up another exchange and give them the same offer.
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Its called business. When the $$$ 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.
No you don't. But you do need to be buying and selling the underlying repeatedly for "some reason".
That "some reason" could be fraud, or it could just be tax-optimization. The important thing is, "wash trading" is the technique of buying-and-selling the same thing at nearly the same time... which has many many applications.
Many of those applications are illegal and fraudulent in a traditional market. So seeing something like 70% of the volume of the real world cryptomarket being wash trading suggests that there's more fraud in the cryptomarket than people generally realize.