Earlier quoted context omitted.
> You do NOT need to change the prices for it to be a wash trade. 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…
My guess is honestly just exchanges trying to get closer to the top of sites like coinmarketcap..
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.