From what I understand, 5GHz radios consume a significant amount of energy and does not travel as far. Awhile back I had to enable the 2.4GHz radio on my router to connect my thermostat, security cameras, kindle, harmony remote etc to my network.
The same applies to other smart watches like the Gear S3 though it allows you to see networks independently from the phone and input the password directly on the watch. Wish WatchOS would adopt that.