Because they're scams.
People will trade their Bitcoins or whatever other currency for altcoins without realizing that they're actually worthless. Once the scammer decides they've collected enough money, they'll shut down their system and everyone who's paid money will lose that money to the scammer.
Topic: How do you get rich by making a new altcoin? (Read 566 times)
How do people get rich by creating new altcoins? 
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