This is the ongoing march towards post-scarcity. We now have enough people with skills, experience and tools necessary to produce a quality indie game and a desire to make one, that the market price is far below the cost of production, and rapidly approaching zero. Essentially, these developers are spending (resources: time etc; although sometimes money as well) to scratch an itch.

And trying to recoup at least a part of those losses by selling the result is not unreasonable, but it should be considered a best-effort optimization. In the end, you still end up paying for the privilege of, essentially, having other people admire your work. It reminds me of some sci-fi story I vaguely remember from a long time ago, about a true post-scarcity society where everything is free, except for other people's attention, which therefore becomes currency. There's nothing else to do for humans other than arts, so everyone is doing that - and now you're paying someone to e.g. read your book, and then they can use that money to pay someone else to look at their painting etc.