I agree, in part: if putting advertisements on your app doesn't help (raise enough money) and selling doesn't work/attempting to sell proves unfruitful, open-so

I agree, in part: if putting advertisements on your app doesn't help (raise enough money) and selling doesn't work/attempting to sell proves unfruitful, open-sourcing is certainly better than just shutting down. Might as well let people have it, if they're unwilling to pay for it, and the work of actually developing the app is already done. Simply shutting down without open-sourcing means that that work was wasted, whereas open-sourcing it might mean that it remains useful to the user community.