While I get your frustration with not being able to order the phone you wanted, like most giveaways/incentives, Google clearly stated that the daydream giveaway was a "while supplies last" type of promotion. So even preordering wasn't a guarantee. It's kind of like bobblehead day at the ballpark - first 5,000 fans get one because they're trying to get people to the ballpark early so they spend more money on concessions, but they're not going to give away more bobbleheads than necessary to generate that traffic. Google offered the daydream view as an incentive to sell phones early and quickly. Clearly it worked since the phone you wanted sold out.
ETA:
Here is the text from the email I received after my order was placed. There's no end date to the promotion, just a start date, and a "while supplies last" period of eligibility. I ordered on the 5th.
*Offer applies to redemption of one Daydream View device with the pre-order of a Pixel device on the Google Store in the U.S. starting from 10/4/2016 and available while supplies last. After a qualifying purchase of a Pixel device, a promo code will be emailed within approximately 4 weeks from the Pixel device shipment date. The promo code must be used on the Google Store before 12/31/2016 and will expire after this date.