A lot of people do these as side projects. A way to sort of build a model train in their basement, free from all the complexities and compromises of "real" software development... They are trying to avoid product managers, sales people, designers, testers... countless others... getting a say in what they build.
And, as a result, there's no business plan past a dream of, "If you build it, they will come." Hard to see any "indie hacker" project that wouldn't be improved with more testing, more marketing, more UX design... more customer research... but most of the time, it's just some guy with a boring day job trying to make $5 selling a widget nobody asked him to build in the first place.
Anyway not to be negative... but like, if you're a small indie hacker who is trying to make a buck, remember that all of the software we use today has a village of people involved in the creation and support of it. If you're trying to do it all on your own... man, that's an up-hill battle. Bring in others as soon as you can.
Then make sure you have a business plan that has the capacity to reward everyone, and be patient. A lot of people in tech... we're early-adopters. This means we do things well before a lot of people even know they exist, and by the time an audience has grown we've already moved on thinking our ideas were a flop. Sometimes they just take a little longer to pan out. (=