Large buy orders are normal and may execute leading to you buying stuff. Wash trades are fakery to make it look like money's being invested when it isn't.

Much easier to generate a pattern or even a sustained history of price rises and trading volume increases via fake trades than try to nudge the price up by spoofing buy orders. Of course, if you're printing your own dollars you can actually execute large buy orders as well, but if you can pump the price some more afterwards, then why not?