Reasons why this has not been addressed, and is unlikely to be addressed in the future:
OMSI itself does not communicate to AI vehicles whether / when the conditions are appropriate for high beam usage (even though supposed to, given that AI_Light has a dedicated value (3) for the high beam; likely a detail planned but never implemented).
As explained in #47, AI vehicles are unaware of their locale.
AI vehicles cannot generally "detect" approaching opposing traffic in order to realistically switch off the high beam.
Reasons why this has not been addressed, and is unlikely to be addressed in the future:
AI_Lighthas a dedicated value (3) for the high beam; likely a detail planned but never implemented).