Imagine saving Bitcoin and earning interests on it when it has gone down and when it goes back up, you are in double profits margin, because it will be too risky to not have a way save your assets and your profits from the falling market and waiting for when the market is favourable.
Yeah , imagine a money printing machine where everyone gets money by doing nothing, how could that be not a great idea?
Remember Celsius, that was a savings account, you would deposit your coins, get interest on it and then....you would have no more coins.
What part of "be your own bank" did you miss?