Why do Tube Amps sound more romantic v SS amps

Harmonic distortion. "Golden age" studio outboard has made a major comeback in the post digital era as engineers try to put back what they lost from analogue tape in terms of distortion..

Its way more complex than that but, and forgive the generalisation, but tube amps with lots of even harmonic distortion tend to sound "romantic".

Probably as they are soft and mellow, lacking any resemblance to realism. 

Great tube amps are anything but soft and mellow.  

Tube amps to.me.sound more holographic. I prefer SS more.

While both can sound fantastic in a good system, with SS you can set it and forget it.  With tube amps, you run the risk of falling down the rabbit hole is changing tubes in the endless pursuit of the perfect sound.  I speak from experience.  I love the look & sound of tubes, I love the sound and ease of SS.