I believe I know why. Remember the issue with LG OLED TV "burn in, where sustained bright images remain, or ghost, into the screen? I believed the Samsung watches are an OLED display, and sustained images might somehow burn into the watch face.
I understand that. But I am personally using Watchface for my faces... The analog AoD is super clean.. 2 white arrows to indicate the time. There is no risk as of burning the screen.. Background is fully black and those arrows move with time.. Just like during day time.. It's not like I have a full JPG on the background that might indeed burn my screen...
I agree with the oled issue but they can make the screen dim out then fade back on every few minutes to "reset" the leds, or have a thin black line "wipe" the screen every few.
Come on SAMSUNG..... Apple has been doing this since thier series 1 watch.
I think there are enough peope interested in this, that you should be able to make this happen.
It's interesting to see that @Mr_Burns thinks this watch SHOULD have come with such an obvious feature. It wasn't until further investigation that he found out it didn't have this option. I would've loved to be there when he found out it didn't come with this STANDARD feature.