Why not the piano as a reference for bass

Piano bass limited in bass energy and duration and thus limited to be used in evaluation.  However, if piano bass is individually important, no reason for that particular person to not target piano bass excellence.

Also, bass preferences can differ - some seek bass energy, while others target better fidelity

The late great Oscar Peterson was gifted a Bosendorfer late in life and he used that low register a lot.  If you can find recordings by Telarc you might hear it.  Also the series "Exclusively For My Friends" originally recorded on BASF in the Black Forest has him playing on a Bosendorfer that I believe has those low notes.   There is also a great recording by Ahmad Jamal entitled "Ballades" on Harcourt of Paris that captures the full scale of the piano magnificently.  

Piano is great and offers something Bass fiddle does not!  Check out recording such as Jin Ju playing Schumann Fantasie in C opus 17 (available on Qobuz) 3rd movement, between 2:20-30 min mark, Steinway 1901 Concert Grand Piano D per the liner notes. 

…the Piano can play bass notes quietly (hence the full name of the instrument - piano forte).  While these low notes may seem anti-climactic for some, the low register of a good piano has an attack to it, especially when played softly, that is beautiful along with tone and overtones, and decay of the note.  A fiddle is generally played loud and consistent in attack, and generally all the low notes all the time (so it’s convenient for use in evaluation as well as what the instrument offers in its own right), whereas piano is playing usually higher notes as well and more often.  So you need the right recording.  I’m not saying a bass fiddle can’t play notes quietly but the piano is pretty unique in what it does.  If a system can produce these notes well, it is challenging.  “One note bass” from some drums or techno or pop music is one indicator of bass but misses a lot in sonority and tone.  

Testing bass response with piano music is a good test- even for integrating subwoofers. 

However it is too limiting and will not reveal other musically important bass qualities that one looks for.  

Great post and comments.  I also wondered about this too. Having access to a Grand and a choir (church) playing weekly, I get to listen to the Grand. I believe based on my hearing, i can get close BUT not the same, no matter what format i use.. Yes the lower registers and overhangs is where there is a noticeable difference.