Celsius does say "While Celsius strives to maintain stable reward rates over tim...

Celsius does say "While Celsius strives to maintain stable reward rates over time, any change in circumstances may bring about changes to such rates, and in some events the rates may drop to 0%" deep in their Risk Disclosure.

https://celsius.network/static/risk-disclosure.pdf

Which is a bit odd- there's no chance you might lose money? How are they making money without risking that the return might drop below 0?