What are we objectivists missing?

I'm totally for people sharing their subjective preferences. I take them seriously and accept that they really do prefer the equipment they say they do under the conditions they are using it. If they don't care about how measurements might correlate to sound preferences that's perfectly ok. No need to do blind testing if you're not interested. 

To answer the OP post, all evidence suggests that under properly controlled conditions we do know how to measure audio signals in a way that accounts for the limits of human hearing. In uncontrolled, sighted settings there are a huge number of variables that change our overall perception of sound quality. Nevertheless, between any two models of speakers  it's easy to measure differences that fall within the known abilities of human hearing, often even between two speakers of the same make. There can be all kinds of interesting interactions between different components, such as amps and speakers, or even pre-amps and amps, and dacs and pre-amps, and even the cables used to connect them. This need not be the case, but it might be preferred to introduce audible non linear responses between these devices to give people room to tailor their sound by mixing and matching components. I believe that almost any speaker in any room can benefit from a little EQ - unless someone just hit the jackpot with the perfect match of room and speaker. Sometimes a little noise and distortion of the right kind can be nice too.

What are we objectivists missing?

The sound of music.

But the hills are alive with the sound of music.