IANARS (...not a rocket scientist), but the maximum thrust needed to rotate the lander, during decent (frictionless free-fall), would be rather low. Vs. the minimum thrust needed to turn it over, against lunar gravity would be far higher.
And, after a hard landing, the RCS system may be damaged - so attempting to use it might result in a RUD event. Or the needed thrusters might be extremely close to the lunar surface (which could direct thruster exhaust and lunar soil back at the lander). Or the RCS might have been given a one-way ticket into a Safe Mode (to minimize potential issues) when the lander touched down. Or...
And, after a hard landing, the RCS system may be damaged - so attempting to use it might result in a RUD event. Or the needed thrusters might be extremely close to the lunar surface (which could direct thruster exhaust and lunar soil back at the lander). Or the RCS might have been given a one-way ticket into a Safe Mode (to minimize potential issues) when the lander touched down. Or...