This is a trope I see commonly repeated but have a difficult time understanding. In what way does (in this case, for instance) an algorithm predicting politica

This is a trope I see commonly repeated but have a difficult time understanding. In what way does (in this case, for instance) an algorithm predicting political bias come to reflect the political biases of the person implementing the mathematical operations behind some gradient descent scheme more so than whoever provided the labels of whatever data it's ultimately trained on?