So they're missing out on roughly 66% of the customer base; look this isn't 2007 anymore, just because it worked for AT&T when there wasn't anything else like the iPhone on the market doesn't mean it will work in 2016; in fact, I'm pretty confident it won't.
People have options these days, if you want to succeed in a highly saturated market, you need to deliver a great product (preferably different and/or better than the rest), you need to market the hell out of that product, and you need to make it available to anyone who wants to buy it.
Pixel doesn't really do anything that any smartphone on the market doesn't already do; and most people are more likely to stay with their carrier than switch for a phone.
In short, if Google's end game was to get "Pixel" to become a household name like any of the other phone OEMs, then they've started out on the wrong foot.
But hey, there are smarter people than me running Google's business, so perhaps I've got this all wrong. I just hope they looked at the fate of the Droid.