My half arsed guess goes something like this:
The issues associated with counter-rotating engines are more applicable to propeller driven aircraft
Asymmetric blade effect (uneven thrust at high angles of attack) does not apply to jets (as much) as the inlet ducting prevents air approaching anywhere but front on; and
Torque effect doesn't apply to jets because torque has to be applied to something fixed to the airframe (cylinder heads for piston or perhaps a gearbox for turboprops) for the aircraft to 'feel' it. Jets have neither as the torque provided by the turbine is comes from hot gas expanding into a free airstream rather than against a cylinder wall.