When Google debuted the Pixel and Pixel XL smartphones last month in San Francisco, they decided to launch it exclusively on Verizon. However, unlike other exclusive smartphone launches, Google has also been selling the device unlocked in their own store, as well as at Best Buy. So the "exclusivity" here is only in terms of carriers that are selling it. Carriers love having exclusives because it means that they have something their competitors don't, making customers want to jump ship. Although these days, exclusive devices aren't as popular - in terms of bringing over new customers - as they once were. But the Pixel and Pixel XL appear to be doing well for Verizon.
According to Wave7 Research estimates, the Pixel has accounted for about 7.5% of activations at Verizon stores since it launched last month. A big part of this is due to the promotions that both Google and Verizon have been running with the Pixel and Pixel XL - one of which is getting the Daydream View for free with a pre-order of either smartphone. Additionally, stores have displays showing off the new smartphones. It's reported that Google spent about $15 million between October 27th and November 2nd on TV ads, promoting the new devices "Made by Google". Meanwhile, Verizon spent nearly $12 million to promote the devices, through commercials. So it makes sense that the Pixel and Pixel XL have been doing well for Verizon and Google, considering the Nexus devices never got advertising like this.
Wave7 notes that with the other carriers not marketing the device, the Pixel and Pixel XL aren't doing as well as they could have been. AT&T, Sprint and T-Mobile don't sell the device, so they likely won't be marketing it in any capacity. But T-Mobile is doing its fair share of promoting the Pixel devices, by offering a rebate of $325 (or half the cost of the device) if you bring it over to their network. This is aimed at letting customers know that the device is indeed unlocked and can be used on any carrier. But as far as spending as much money on marketing these devices as Verizon has, it's very unlikely that the other carriers would, especially since Verizon has that exclusive on selling the devices.