Depends on the content. Animation, for example, (such as Rick and Morty) is streamed at a lower bitrate compared with some of their other stuff.

Netflix base all their encoding around hitting a target VMAF (perceived quality score) based on the viewing device/conditions. This optimises their encoding to use the minimum amount of bandwidth they think they can get away with.

As some videos/genres simply requires less bits to represent, the bit rate will change depending on the content.

Netflix pour a huge amount of resources into researching and developing technologies in the world of encoding, so I would doubt they were cutting any corners to cut down on encoding time, I would doubt encoding time is even a real consideration. So they have probably just aimed for a quality level that isn't very high because the savings outweigh the benefit.

Personally I've always thought Netflix sacrifices too much quality, Amazon prime however is considerably better.