Why do tube amps generally have larger sound stages? maybe its a harmonic effect some amp do them well some don't. Is it distortion effects, even/odd order effects?
clarity maybe, but I've heard some older vintage tube gear throw a huge sound stage with out great detail and clarity levels. so really doesn't hold up in my experience.
Even though the OP used a YouTube video as an example its still a valid question that many of us have experienced when trying new gear.