SBD was meant to be a regulated coin which was to be pegged at $1 and it is reacting to what it was meant for while Steem is not regulated as it can go up any time and at the same drop down like Victoria waterfalls.
That's because while Steem is a liquid currency, whose value fluctuates just like any other coin, SBDs or Steem Backed Dollars were designed to be pegged to the US Dollar. So, while the price of Steem will be affected by market forces, SBDs will always be valued somewhere around $1 US. SBDs were designed this way to give businesses and other individuals who are not used to the volatility of cryptocurrencies a more stable and somewhat familiar coin to trade with.
Nonetheless, it is important to note, that the current mechanism pegging SBDs to $1 US is not perfect. That's why it has dropped to $0.8 US and increased to up $12 US in August and December 2017, respectively. This, however, is going to be addressed by the upcoming Hardfork 20 on September 25, which should make the SBDs more stable at $1 US.
SBD is not getting printed now because of a built-in safety net feature in the steem blockchain. So if the debt ratio (total SBD in existence / total Steem market cap) goes above 2% author rewards will paid only in Steem and Steem Power. We are currently past 5% debt ratio and that is why SBD is not getting printed any more.
So that makes the availability of SBD limited, to help it resist the market movements. However, steem is getting traded in exchanges and is directly controlled by the price movement of the BTC market. So its getting affected.
There is some important changes proposed for SBD in hard fork 20, by @timcliff. Feel free to go through more information on SBD and the proposed change in this post made by @timcliff
Hope this answers to your question ?
SBD is a stablecoin pegged to the US dollar. How is this done? The Steem blockchain allows for SBD to be converted to 1 USD worth of STEEM in a process that takes 3.5 days. The delay is there to prevent the system from being gamed by exploiting short-term fluctuations of the price of SBD. This is the foundation of the USD peg of SBD. Another aspect of the peg is that the rate at which SBD is issued is limited by the value of all SBD in circulation in terms of USD. When that value (the market capitalization of SBD) exceeds 9% of the combined USD value of all STEEM (the market cap of STEEM) in circulation, the system starts giving an increasing percentage of liquid rewards as STEEM as opposed to SBD until at 10% the printing of new SBD stops completely.
If the market cap of SBD reaches 20% of the market cap of STEEM, the conversion mechanism stops working. When that happens, the peg is be broken and the price of SBD will plummet as a result.
Sbd is like Tether 1SBD = 1 Dollar this why is resisting and the steem blockchain this time not dropped to much sbs only steempower