From July 1st Pokemon Go will no longer work on the Apple Watch.
Niantic’s support page for the upcoming changes lays out the reasoning for the move away from Apple Watch:
Because Adventure Sync allows Trainers the option of tracking their steps, earning Buddy Candy, and hatching Eggs in one mobile device rather than 2 separate devices, we want to focus on building Adventure Sync so that Trainers will no longer have to split their gameplay between 2 devices.
The Apple Watch version of Pokemon Go tracks your steps and sends that data to the game. The app also allowed players to collect items from PokeStops, something that Adventure Sync doesn’t do. Pokemon Go players with Apple Watches could also receive notifications when Pokemon were nearby, although they needed to open the app on the phone in order to catch them.
Niantic has made this announcement just before the launch of watchOS 6 which is reportedly to bring an Apple Watch store.