That's because a garage coder is coding for a much smaller niche market.
Like a specialty custom car... doesn't cost more to design and make than say a new line of Hyundai, but it's going to be more expensive because a garage coder can't rely on a billion dollars of promotion and distribution deals and basically knowing he's gonna sell a billion of them. Developer has to charge more to recoup his cost otherwise it's not worth it and nobody will ever write custom apps.
Also an app --regardless of the cost of development-- has more value to the niche user of that app than any game usually. So supply and demand wise --it makes perfect sense.