it has to do with one piece being read primarily by nerdy teenagers who have no idea what good music is. that, in addition to p-funk not being the absolute END ALL of music that encapsulates one piece's spirit or anything–it's just your personal preference.
why aren't amv-makers setting one piece to afrobeat or shoegaze or folk? the list could go on. short answer: the majority of people making amvs are either unaware of what p-funk is or don't like, like the majority of people in general. honestly, why not just have a big thread with a list of music genres you'd like to see one piece amvs set to? maybe some magnanimous person who likes making them will give it a shot, or be inspired.
an even better option might be to just listen to whatever music genre you prefer while reading the freaking manga. problem solved. frustration ended.