It sounds like imprecise language is used in those simulator controls. The N1 (fan) shaft and the N2 (core) shaft both have turbine stages at the back end. The rotation of the two shafts is not mechanically connected. The core being seized or simply not turning due to accessory drag at low airspeed will not directly mechanically affect rotation of the fan shaft. It sounds like the "turbine seizure" selector you describe simulates a stopped core shaft and tries to simulate some sort of N1 system mechanical failure. It's not clear what actual mechanical failure the designers were trying to simulate. The heavy airframe vibration they simulate with N2 at zero obviously is intended to represent damage to the N1 system, like out of balance or bearing failure. Failure of the N2 turbine that releases parts in the gas path often will cause heavy damage to the downstream N1 stages.