Because it's all about context. It would make no sense to use a term contrary to its accepted definition of its context.
I'll accept that you have a different definition, but I still I disagree as to that intro being wank. It's a slow built-up intro, increasing in intensity to set the mood of the song. In a 24 minute song, I don't see 4-5 minutes as being excessive or self indulgent any more than for example the 3 minute outro solo by JP for TBOT.
I get that but based on your use of ratio of intro to total song length then Six Degrees could have a bland ethereal 7-9 minute continuum intro and that'd be just fine. I have no problem with establishing mood but the when the pacing causes me to lose focus and become frustrated at the waste of time it's turned into I draw the line. At least after those 4 minutes(well 3:48 anyway) he brings in that melody that begins to give the song some life.
What I don't understand is how many people on this forum slobber all over 8vm's intro but virtually everyone will pan Opeth's much shorter outro to Dirge for November for it's "redundancy."
Where is anyone slobbering over the intro? Some people like it, some don't. And it's bland in your opinion, but to me it's a great moody build-up to the song, building up intensity over an interesting and unique underlying chord progression. I respect that you don't like it (plenty of others who don't, and I skip it occasionally too, no big deal), but I don't think it's wank any more than the intro to Trial of Tears, the mid-section of TCOT, or any other lengthy outro solo by JP like TBOT.