According to DMCA, to avoid liability the ISP must not financially benefited from the infringement. But ISP is always making money in one or many ways from infringement (ads display, subscription, marketing, publicity, traffic) Especially when the infringed content is popular, the revenue must be there more than usual.
so how can ISP ever be innocent?
Addition from comments:
I think the key for this is DMCA does not specify indirect or direct benefit of ISP. So lawyers can always say that ISP gained "a benefit". Also most of shady file hosting sites their main purpose is obviously make money from illegal content in a short time until reported. When someone upload a popular illegal content on youtube, gets 1 million view in a day then deleted by google. Google already made big ads revenue, which is the main business model of the website. That is completely a direct benefit out of it. With full purpose and intention of Google.