If I had to guess, I would say that Comcast had a huge proportion of 'users paying Netflix money and which live in an area where there is no broadband competiti

If I had to guess, I would say that Comcast had a huge proportion of 'users paying Netflix money and which live in an area where there is no broadband competition'. If the problem with Comcast is that their network is congested and users can't switch to another provider then it doesn't matter whose fault it is, those people are going to leave regardless. Note that Netflix is only showing these notices in areas where Verizon has competition to which their customers can switch, which lends a lot of credence to the idea that 'ISP switchability' is a key factor guiding Netflix's behaviour.