I expect this is because people are panic selling!
But logically they shouldn't, because if the system works correctly, then SBD should eventually be expected to trade around $1 again (once the panic is over!)
This is because the wallet provides a 'convert to STEEM' menu option which should give you around $1's worth of steem in 3.5 days time from when you request the conversion.

But you can read more about this here:
https://steemit.com/faq.html#Will_1_Steem_Dollar_always_be_worth__1_00_USD

So, I personally would never sell SBD for much less than $1, but instead just wait for it to return to roughly this value...or else use the 'convert' function.