If we accept that ChatGPT has a liberal perspective, consider this: ChatGPT was founded on the Internet. It reflects the perspectives it found there. To the degree that the Internet reflects the real world, any liberal aspect of ChatGPT reflects reality and is not a bias. It's truth.
95% of people are probably centrist and neither comment and neither create content.
It's the 5% of the extremist that generate 99% of the content.
So if those 5% of the extremist are leaning more towards one end you'll get the illusion that "the internet is mostly liberal", while in reality that "mostly liberal" is generated by sub 5% of the actual population.