If ISPs don't shut down people's accounts they'll get sued for billions in fines.
There are still open court cases against multiple ISPs for not cutting enough people off from the internet. So far, courts have agreed with the RIAA/MPA who paid good money for the laws we have.
Yes, the media industry is certainly more to blame here. Although, the current ISP oligopoly means that there are less companies to sue or otherwise bully. And it doesn't help that some major ISPs are owned by companies that also produce copyrighted content they want to protect.