The NSA which is supposed to be looking after national security was revealed by Snowden to be engaged industrial espionage in Germany. That thows their motivation into question. If they were spying on Germany for industrial secrets then their motivation for collecting that meta-data on American citizens looks even more sketchy. I always wondered how they were going to use that meta-data effectively given that any useful information would be hiding in there like a needle in a haystack and that the NSA failed to stop the horrific bombings in Boston.
If they are stealing information on industrial secrets chances are they are selling the information to certain companies who would benefit from these secrets. That raises the question of whether or not they are selling the metadata or economic analyses thereof to certain companies or individuals who would stand to gain from the information. Perhaps as insider trading, by using it in the stock market!