I don't think it's really the pixel art that makes this AI piece resonate with people. It's that the general art style espouses classic fantasy paintings and utilizes traditional image composition to give a huge sense of scale.

The sad reality is that modern PBR games have a lot of trouble with lighting and contrast. Everything looks washed out, foggy, and equally dense with detail. The images look closer to photographs of mundane mountains, than fantastic worlds to explore.

Art has an innate exaggeration and representational nature to it that pixel art and low poly games somewhat capture. Even PS2 games and 2005 PC games had this feeling because their textures were painted on... but today's games feel too close to real life, but not close enough and thus fail to have the magic of a painting or the joy of a real mountain vista.

The AI images are popular because they remind people of the artistry we've lost in the digital age of hyperrealism and graphical fidelity.