The reason is that it all depends on the style you're plaing, and sometimes even the exact song. Every make of guitar has a slightly different sound to it. The Fender Stratocaster has a great, nearly ubiquitous sound. I love the way Paul Reed Smith's sound. The Les Paul from Gibson is highly versatile. You've got solid bodies, archtops, single-coil, humbuckers, different wood types, different kinds of tremolo systems, etc etc etc.
Personally, I have a Fender Stratocaster and a PRS 24-fret model. I love the PRS for a more mellow sound, or for really obnoxiously loud distortion. The strat I love for bright, bitey soloing. I could not use the Strat for jazz - it would sound awful (to my ear, anyway), and some rhythm things I play just sound like crap on the Strat, too. Likewise, if I want a really clean sounding solo, I won't use the PRS.
Attention: NOTHING on this site may be reproduced in any fashion whatsoever without explicit consent (in writing) of the owner of said material, unless otherwise stated on the page where the content originated. Search engines are free to index and cache our content. Users who post their account names or personal information in their questions have no expectation of privacy beyond that point for anything they disclose. Questions are otherwise considered anonymous to the general public.