Well in the case of Celsius they are putting use funds into things that the user might not know about. Such as stETH which provides yield but can't be withdrawn back to eth until months down the road so if stETH starts trading at a discount like it did recently then you can't actually get all the money out for redemptions. I believe they also put funds into Terra which they lost as well. So basically Celsius advertises a certain yield but is a black box after a user deposits funds and they might put the funds in things a normal user would never agree to if they were aware of it.