ISPs may have regional scale, but the big ones, Comcast, Verizon, etc. run significant parts of the internet's uplinks and switching infrastructure, and you can bet it's not just outgoing traffic they snoop. They have been caught with their fingers in the cookie jar many many times. At least with FB and Google you can choose not to use their services and block their trackers. You can't choose where your packets flow, and in many regions there is literally only one option for bandwidth because of local government sanctioned monopolies over the infrastructure.
None of those transgressions resulted in visible, tangible harm the way Facebook's have.
Would I love to go after the ISPs? Sure. But going after them is falling for policy perfectionism. Facebook and Google are in the crosshairs. This isn't a choice between doing something about them or the ISPs; it's a choice between doing something about them or not. If privacy advocates want to do more than talk, this is the time to show discipline.
One, this is trivially defensible against with a VPN. Two, ISPs have regional scale; Facebook and Google are international. Three, we have actual evidence of Facebook repeatedly dropping the ball and causing tangible harm on multiple continents. We don’t have the latter for ISPs nor Google (in respect of the latter, outside YouTube).