The Indian political parties boycotted the Simon Commission primarily because there was no native Indian member in it. This meant that the Commission, which was appointed by the British government, did not have any representation or involvement from the Indian population.

Option 1 states that the Commission was appointed by the British government without consulting the Indian political parties. While this is true, it is not the main reason for the boycott.

Option 2 suggests that the members of the Commission were not sympathetic towards Indian nationalist aspirations. Although this might have been a reason, it is not the main reason for the boycott.

Option 3 suggests that the Commission was unduly biased towards Muslims. However, there is no evidence to support this claim and it is not the main reason for the boycott.

Therefore, the correct answer is option 4, as it accurately reflects the main reason for the boycott - the absence of any native Indian member in the Simon Commission.