I was looking at Exodus.io and specifically it's fee structure to try and see how they make money, when I stumbled upon this:
How does Exodus make money?
Exodus generates revenue from a small portion of the spread on asset exchanges. Although spreads can vary greatly based on market conditions, typical spreads range between 2% - 5%. The exact amount and rate you’re getting will be listed on the exchange section of the wallet.
In highly liquid markets, spreads are tighter, creating a lower cost. You can learn more about spreads here: https://en.wikipedia.org/wiki/Spread_trade
Spread trading sounds very interesting, but even the description has my scratching my head:
In finance, a spread trade (also known as relative value trade) is the simultaneous purchase of one security and sale of a related security, called legs, as a unit. Spread trades are usually executed with options or futures contracts as the legs, but other securities are sometimes used. They are executed to yield an overall net position whose value, called the spread, depends on the difference between the prices of the legs. Common spreads are priced and traded as a unit on futures exchanges rather than as individual legs, thus ensuring simultaneous execution and eliminating the execution risk of one leg executing but the other failing.
Sounds very interesting and something I'll definitely investigate when I get a free moment.