Different styles and different clubs/schools do things differently, it doesn't make it wrong to take a long test nor does it mean it's wrong to do a quick one because the student has already demonstrated ability.
For my test it was a matter of having a lot to demonstrate before the board, we have a big curriculum including ground work, weapons, techniques, kata, combinations, Ohyogumite, Kihon kumite, free sparring, self defence and teaching. That will easily take a day to show.
Stances alone we have 5 'natural stances, 6 'even' stances, 11 'uneven' stances and 4 'others'. All 15 kicks are done off each leg some also to different heights ie one to knee, one to middle one to head as well as jumping kicks which are done two different ways. We have 15 'arm' blocks, as well as leg blocks sweeps etc. There's also body movements to show then there's renrakuwaza ( combination techniques) done in line as well as set ones...ipponkumite and yakusoku. a lot is done in line work which saves some time but much isn't. The sheer volume of techniques etc we have to show makes it a long day.
The point too was that we enjoyed the day, yes we knew we had our instructors confidence and they knew we were prepared but going into something like that gives you a huge sense of accomplishment and confidence coming out of it. Perhaps you could call it a rite of passage, perhaps not but it certainly gave you a thrill to be presented with your black belt afterwards. It may have just been us doing what you do, showing off what we know, but because it was a long and encompassing day we really felt we'd worked hard. Did we need to show every techniques? Probably not but it felt great being able to remember and execute every single one of those movements. We would never do that again, not for subsequent gradings. Do people fail? Yes.