To take money away from you and others who have invested, and then use that money to enrich themselves. BTW you're absolutely spot on: most altcoins are indeed fake and scams, the owners basically create them only to make money for themselves, they have zero use cases, most times plagiaraized whitepaper, impostor team of developers, etc. If you don't want to be scammed with fake/scam coins, then only invest in Bitcoin and forget about altcoins, there are so many of them, so to find a productive one is as good a task as looking for a needle in a haystack.