Because it is not mission-critical in the first place. If you think the flight plans on the iPad is the sole critical factor in the overall flight operation, yo

Because it is not mission-critical in the first place. If you think the flight plans on the iPad is the sole critical factor in the overall flight operation, you're mistaken. There are fallbacks, there are fallbacks even for the fallbacks and finally, the pilots themselves are trained in the event of total failures on all ends. In addition, it was a software glitch. We don't know what kind of glitch it was but if it was, it doesn't matter if they were using proper-graded billion dollar worth of products, software glitches exist everywhere.