You, as a consumer that does not have an iPhone, cannot walk into a store and buy an Apple Watch that is cellular enabled/activated. You have to have an iPhone to have it provisioned and configured.
In my perfect world, I purchase a cellular enabled Apple Watch, login to some eSIM provider portal or Apple, provide them my MEID and then the watch provisions. Then I can configure notifications, apps, etc... via iCloud.com or from my MacBook.
I honestly do not need a mobile phone at this point in my life and my Apple Watch is just absolutely perfect for my day to day needs outside the home.