Why don't my iPhone locations automatically appear on my Apple Watch?
ETA for Apple Watch utilises iCloud to backup and save all your locations and lists. If you delete the app, simply reinstall and all you data will immediately populate.
To utilise this great feature users need to add locations into both the Apple Watch and the iPhone. If you've spent some time loading locations into your iPhone and open the Apple Watch to an empty screen then don't worry. Simply bring your iPhone close by and choose the option to 'Import Locations'.
More information on how to import locations from your iPhone are via the relevant article linked below.