I actually don't think anyone used it. The issue is Google didn't allow you to go back and add it within a certain time of your purchase. It also wouldn't let you purchase it at checkout with a new Pixel if you were already paying for one of the subscriptions it was composed of.
I think the other issue is most people aren't upgrading back to Pixel and most of their users are new and unsure if they will continue with Pixel. Personally, meh. Google kills something that isn't profitable and it's clear it wasn't being used as intended or gaining as much traction as they thought it would. On top of that it was just kind of a mess. If I buy a Pixel from Google why don't I have a week after my purchase to at least add Pixel pass.
I love my Pixel and I have had every Pixel except the 5. I will continue to buy them with or without this pass.