Bitcoin/Ethereum have PoW, which cant be easily reproduced, but Iota has no such thing, it can easily be cloned, and tokens distributed at will. Bitcoins are generated, so cannot be distributed without investing alot of time or hardware up front.
Clone bitcoin and set a fixed mining difficulty to 1 and the premine them all. I can distribute all of them at will as well.
Besides, IOTA does use PoW. Just no block reward.