This is why：

            if( has_hardfork( STEEM_HARDFORK_0_14__230 ) )
            {
               // This block limits the effective median price to force SBD to remain at or
               // below 10% of the combined market cap of STEEM and SBD.
               //
               // For example, if we have 500 STEEM and 100 SBD, the price is limited to
               // 900 SBD / 500 STEEM which works out to be $1.80.  At this price, 500 Steem
               // would be valued at 500 * $1.80 = $900.  100 SBD is by definition always $100,
               // so the combined market cap is $900 + $100 = $1000.

               const auto& gpo = get_dynamic_global_properties();
               price min_price( asset( 9 * gpo.current_sbd_supply.amount, SBD_SYMBOL ), gpo.current_supply );

               if( min_price > fho.current_median_history )
                  fho.current_median_history = min_price;
            }