Well, I am not sure, it's either a bug or they are trying a scheme/scam. Even if you try to sell SBD on the site, there are no people that would really buy your SBD for 21$ while there are sites where you can get 10+ times cheaper. I heard rumors that the site is pretty buggy and had issues in the past.
Later edit: Register is off for me, I think they don't even accept new users.
Coinmarketcap took off hitbtc from the markets section on SBD for the past 3-4 days, but now they are back. SBD was even at ~70$ on HITBTC yesterday.
HitBTC is well know for closing their wallets for maintenance. Every time they do, the prices of those coins skyrocket. As of a day or two ago, they closed SBD wallets for maintenance. They are becoming quite scammy, if you ask me. I'll never use them.
Thanks for the answer! It helped me understand,but yes, I am still confused☺
I am a little bit confuse too, that price it's not right, no sane person will buy SBD for that price. Someone is gaining something from that price.