Unpairing and repairing IS a big deal. It takes about 20 minutes if nothing goes wrong, and that's a big if - mine crashed on unpair, and I had to set the whole thing up as new. You lose your app layout and everything in Apple Pay, and you may have to toggle some notification settings or reboot your phone to get everything working right.
I can't see anyone wanting to spend 20 minutes pairing and setting up the watch/Apple Pay on a regular basis when you can swap the band in a matter of seconds.
As for Apple realizing folks won't want to run in their editions, I considered the rose gold and leather band combo, and I'd just pick up a white sport band for workouts. Sweat's not going to damage the gold, you just clean it up when you get home, same as with the stainless.