I don't believe they did, actually. Per my understanding, the Whirlpool feature in Sparrow was just an implementation of the open protocol, simply allowing you to join the Samourai mixing network without using Samourai software. 

0xIlmari

I think Sparrow used to get money from mixing, but they removed that future.  Still, I think that was more of an add-on; really, the motivation was as you describe.

elvismercury

bitcoin

What is the business model of a BTC Wallet provider?

criptopanas

Sometimes people just make useful software in their spare time and make it free and open source for the entire world to use.

This is the case with Bitcoin itself, but also Sparrow, I believe.

If the software is particularly useful, some people will simply donate to the effort, which can lead to the developer(s) being able to work on the project full time. 