most of times these are just "Pump and Dump" scheme.
Newbies see price growing and good volume, and they decide to invest in the coin... but they dont' know that some one is ready to dump all coins!
I don't think they pump a scam coin for money laundering..... I can't see any advantage for a trader
there are some scientific papers about this argument e.g: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3267041