Why would you or anyone buy a tube amp?
For the warmer presentation that tubes generally afford, with a rounder sound and a more coherent sound than S.S. in general...
As always it seems, the higher price one pays, usually this too affords its own degree of higher resolution with Headamps in general, in my experience.
For instance, in comparison to the Heed Canamp, which had more raw power than my Corda Headfive as well as better low end extention and promenance of bass notes, the mapletree showed the Heed to be glassy and cold especially in its midrange. Whereas, the strenth of tubes and the MAD in particular was having the same drive and power(gain), while this amp produces an expansive soundstage and life-like vocal presentations.
Experimenting with the power tubes to change the sonic signature of tube amps provides a direct influance on tone control, dialing up the bass or bringing the midrange into even more promenance. This is both utilitarian and interesting to change up the sound, or to better match a particular headphone, or even treat the music, which in my opinion, only 50% of which is well mixed and mastered anyway and tubes do tend to hide the digital nastys of these sources. Yes, its coloration, but it sounds so very right when applied to particular recordings, allowing for their further enjoyment with a more analogue toned sound, IMO...
I had to step up to the Opera to find an amp that could replace my listening preferance of the Mapletree...
Anyways, these are some of the reasons folks upon hearing and comparisons, choose to listen thru tube amps, IMO...
Hope this helps your understanding somewhat, without the advantage of auditions...
Of course, buying used is the best way to long term audition a piece for evaluation, IMHO
Good luck~