Why did Old Prussian retain a neuter gender when Lithuanian and Latvian did not?

Old Prussian retained a neuter gender because it preserved many archaic features of the Proto-Baltic language that were eventually lost in the East Baltic languages, such as Lithuanian and Latvian.12

While Lithuanian and Latvian evolved to utilize only masculine and feminine genders, Old Prussian maintained the substantive neuter gender inherited from its ancestor. Examples of this preservation include the Old Prussian assaran (lake) and lunkan (bast), which correspond to the masculine forms ežeras and lūnkas in Lithuanian, and ezers and lūks in Latvian.12

Old Prussian is characterized by its retention of a greater number of archaisms than either Lithuanian or Latvian, placing it in an intermediate position between the East Baltic group and the Slavic languages, which also maintain three genders.123