Because when POS happens, AFAIK the minimum amount for you to become eligible to stake must be 32 ETHs.
32? That's an insane lot just to start earning passively and the returns only start from 4% onwards.
That 32 ETH minimum amount to be eligible to stake sounds ridiculous in my opinion. When ETH was proof of work, you can mine it in less than $100 VGA and still profitable if the electricity cheap enough. That's cost like half of an ethereum right now. If we take 32 ETH and covert it to roughly amount to set up mining hardware, the curtain of proof of stake clearly higher than the old proof of work.