I agree with you that 10 years is more than enough time for corporations to turn a healthy profit on something (not that they can't continue to make money off of works after something has entered the public domain) but this wasn't a small victory. If every ISP were at risk for endless billions in damages because of what their users did it would mean that ISPs would be forced to give in to the RIAA/MPAs demands to permanently terminate the accounts of internet users over completely unproven (and often inaccurate) accusations of piracy. It's worth noting that cox was actually doing this in a limited number of circumstances, and the media industry still wasn't satisfied.

The media industry insisted that they needed the power to get people's accounts terminated even though it would have left many people, including fully innocent ones, cut off from the internet entirely. This was a big deal and I'm honestly surprised to see the supreme court do the right thing.