Yeah when Apple’s home measurement tool for the solo loops turned out to be horribly inaccurate, they were flooded with a ton of returns and didn’t have nearly enough solo loops in stock to cover them. So, they sent people free sport bands in Surf or Cactus so they would have a band while they waited for the right size to come in. I’m assuming Apple offered those colors because they had extra supply or because it was easy to ramp up production.
What I am guessing happened is that a good chunk of S6 buyers were coming from a previous gen Apple Watch and already had other bands they liked better. So, a bunch of them took their free sport band and threw it up on eBay hoping to make $30-$40 off of it. That’s why there are about a million Surf Blues on eBay/Mercari right now.
According to leaker Jon Prosser, Apple has reversed its requirement for users to return their Apple Watch Series 6 if its Solo Loop, or Braided Solo Loop, isn't the right size for them.
appleinsider.com