I think the problem with the Big Problems (tm) is that solving them is not a One Solution Big Reward job. It is millions of different tedious little problems. Solving a few of them will not give you anything.
Example: Decreasing energy consumption of mobile devices. Is that a Big Problem? I think so. How do you do that? Lots of little tweaks and fixes on various layers (software, hardware, interdependencies, etc). Lots of 0.1% improvements. After a few years you get the new iPhone and it is 10% better with energy. Of course, you only see 5% improvement, because additional features ate up the rest. Note that those little efficiency improvements enabled those additional features. However, nobody really appreciates the junior engineer who was responsible for 11 of those 0.1% improvements. Not even she herself finds that amazing.
Example: Decreasing energy consumption of mobile devices. Is that a Big Problem? I think so. How do you do that? Lots of little tweaks and fixes on various layers (software, hardware, interdependencies, etc). Lots of 0.1% improvements. After a few years you get the new iPhone and it is 10% better with energy. Of course, you only see 5% improvement, because additional features ate up the rest. Note that those little efficiency improvements enabled those additional features. However, nobody really appreciates the junior engineer who was responsible for 11 of those 0.1% improvements. Not even she herself finds that amazing.
Am I too dark?
(disclaimer: I know nothing about actual iPhones)