Due to risk of compressor stall.
In order for the fan (and thus the downstream compressors) to work properly, the airflow needs to be smooth and straight.
For the most part, the nacelle, the diffuser (cone) and stators all serve to smooth and direct airflow to the compressor, but in the case of crosswind, low airspeed and high power setting the airflow may be disrupted to the point of causing a compressor stall.