It doesn't have to. However, headphones are products of technology, knowledge and skill, serving the same basic purpose: reproduction of music in a satisfying way. As such, comparisons are unavoidable and as a matter of fact are the essence of this site. When we start talking serious money, comparisons are very useful or necessary. If we just wanted info on what's available, the manufacturers' sites are there. But we all know that their claims can be anything from accurate to "bold" or even misleading. Personal taste does not invalidate careful or long term tests and comparisons. For many here the most accurate AND musical reproduction is the "holly grail" of headphone technology. These two targets are not that different or "incompatible" as some want us to believe, to sell better the differentiating "perfume" of their products. Quite the opposite, I think. Of course, issues of different ear/head shape or inner ear differences, along with long term listening habits can alter the perception of sound and result to "different hearing" (also different comfort evaluation). That is where as many users' experience as possible become of importance when personal listening before buying is impossible.
In the end, when we feel that we need to replace a headphone (or a source) for something better, how do we settle to a new unit? Is it not with a systematic or automatic comparison? Whether it is a very short one or a long term one is only affected by the circumstances and individual needs.
Ed. My reply to the above post was written for an initial form of it. (Besides that, not everyone choses to listen to different kinds of music with different headphones.)