Job Market Paper

I hate the term "Job Market Paper".  It is somewhat unique to the  discipline of economics and finance and refers to the working or published paper that graduate students put up for assessment while applying for jobs in academia. I don't understand what so special about the JMP. What about other papers that the student may have written during his PhD? Are they inferior to the JMP? Yes, it turns out.'The JMP is an original piece of research by the applicant that constitutes their best research to date. It is meant to serve as a signal of the candidate's potential for becoming a good researcher.'  I am sure every researcher likes some of her work more than others, but such opinions are necessarily subjective. Someone else might consider another piece of her work as being better than her JMP. The idea that you can have an unambiguously best piece of research, just like a sprinter has a best time, sounds bizarre to me. Another example of blind positivism in economics--the idea that brilliance doesn't lie in the eyes of the beholder but is an objective characteristic of  the work or the person being judged. Call me idealistic but isn't one supposed to do her best at every research project one undertakes? Or is one allowed, even expected, to do sub-standard research for non-JMPs?