I believe that one factor is their form of locomotion.

Source: https://www.dailyadvocate.com/2023/09/09/finding-value-in-creepy-animals/

The executive adds that, while Amazon Robotics has thus far exclusively traded in wheeled locomotion, legs present a good deal of possibility.

Source: https://techcrunch.com/2023/10/21/humanoid-robots-face-their-first-major-test-with-amazons-digit-pilots/

The same applies to clothing, housing, mode of locomotion, etc. The latter, are all part of wealth and the former are part of development.

Source: https://allafrica.com/stories/202301270040.html