"Larger amounts most likely have less good privacy properties, due to their token denominations being rare. Cashu uses fixed (power-of-2) token denominations to create a hide-in-the-crowd effect. But the larger a token gets, the more likely it is that fewer and fewer of them exists, and at some point there is no crowd to hide anymore. If there is only one token of a specific denomination, it can always be linked back to its creation."

https://docs.cashu.space/faq