This is a guess. Suppose many Nostr relays charge a fee, requiring users to pay 1 ecash sat for each note they send. At the same time, many mints issue ecash, and these mints are more likely to opt for a model that allows for redemption back into LN sats. Nostr relays would choose to accept ecash from many mints. Both Nostr relays and Ecash mints are service providers, making it unlikely for a monopoly to occur.
Discussion
Here's a question. Are ecash tokens capable of decomposing? Using fiat as an example if I exchange for 20 dollars am I getting:
A) one 20 dollar note
B) twenty 1 dollar notes
And whatever note I get can it be incremented down any further?
I guess Cashu now supports decomposition down to 1 sat, and may allow for less than 1 sat in the future.
Cool. I would definitely prefer to exchange 100 sats for 100 ecash sats to the pay out as needed than to request a single ecash sat as needed.
Forgot to include nostr:npub12rv5lskctqxxs2c8rf2zlzc7xx3qpvzs3w4etgemauy9thegr43sf485vg on my initial question.
But there's a well-known business model where you only allow one-way trade for your tokens. It's very lucrative if you have volume, as people over buy and then can't trade out easily. Think parking meter minutes, in-game currency, mobile phone credits, gift cards, airline miles....