With the Chromebook obsolescence fallout and the decision to extend software and security support for those recently, one would assume that the Pixel may be subject to similar thinking within Google. But the sales volumes of Pixel phones are a lot lower than Chromebooks. Google doesn’t seem to generally handle hardware quite well.
You can see the full OTA history for every device going all the way back to the Nexus S:
https://developers.google.com/android/images
Note that there's no weird gap around the transition from Nexus to Pixel, both were supported concurrently during the overlap.