For some, the journey isn't always about the final destination, rather it is the journey itself that is the reward.
Enough philosophical crap. While I have not published any apps for android or iOS, I have learned how to start programming for android for fun. If I actually had time to finish some of the ideas that I had, I most certainly would publish them. I would not expect to make a lot of money on it. I certainly would not expect to replace my current income with app development, since as you so eloquently put, the pay off is only a few days of salary. Part of the reason for publishing it however would be just to learn the process and the sense of accomplishment.
Anecdotal story time. Our company recently interviewed a guy who did some amazing professional level FPGA development on his own time. He went so far as to pay for a double sided board that he routed himself, had DDR3 ram, various video codecs, and an FPGA which had a BGA for a footprint. This are pretty complicated things to do and not necessarily cheap to fab, let alone as a hobby when you are paying for it yourself. While he might think about marketing this product in the future, he mostly did it because he thought it would be cool. Sure enough when he showed us the final product, it was most certainly cool. I would tell you who this is, since he has a you tube channel, but we are still trying to hire him.