The only reason is that the Muslim Brotherhood is in the way of the Saudis spreading Wahhabism throughout the globe.
For the Saudis and the Gulf petro states, the Muslim Brotherhood in power has become a menace to regional stability and even to the long term survival of their regimes. This is consistent with the history of Islam and its recurrent religious revivals and messianic leaders who discomfit and threaten the established order.
Bandar is admitting that the Saudis are using jihadis as useful idiots to overthrow Assad, but that they will not allow them to rise to power in Syria, just as the they did not allow the Muslim Brotherhood to rule Egypt. Once the useful idiots have served their purpose they will be dispensed with, as useful idiots always are.
It would be better for Russia if Chechen jihadis went to Syria to die in the desert fighting other muslims, instead of targeting Russians. Putin is too busy hating the USA and trying to get revenge for the Cold War to do what is best for Russians. Instead Russians suffer and die so Putin can prop up Anti-American regimes.