You’re a hacker news reader so more like an “elite” user of technology. Most people aren’t and won’t do things like read the Apple Watch EULAs on the watch, setup payment cards on the watch alone. I don’t think it’s even possible to setup the eSIM and number syncing without the phone yet. It seems tied to your phones IMEI.
Maybe Apple would make a UX for the small minority of people like yourself, but they already have a lot of stuff going on and I guess it’s not financially viable to satisfy everyone in all situations.