Just from a pure money making business perspective... Why would a compmany side with, collaborate, or do business with any organization that wants to sue/disconnect it's customers? Are they looking for less revenue? Do they have too many customers?
This completely boggles my mind.
It's business, so it is simple.
The ISP's are either afraid they will lose money, or they stand to make money. That means they are either being threatened by the RIAA or the RIAA will be working with the ISP to somehow make some money, perhaps with future exclusive content or some other proposed value-added service.