Because 5 days is enough, by my reckoning, to adjust to a 5mg drop in dose. Ideally a slow taper should contain good days (i.e. the 5th day after a drop) but no "stagnation days"; hence I haven't said drop 5mg and stay on that for two weeks or a month, before making the next drop. In such a case all the days after the first 5 or 6 are essentially "stagnation days", where no progress is being made.

We all know the saying "the devil makes work for idle hands". If we're sitting around doing nothing, with the end a long way off, we're likely to have a "fuck it" moment. I only know of one person who succeeded with a super-long (18 months) taper. But before he started he had already succeeded in the sense that he had reached an "enough is enough" point, which is of course far more important than the details of the individual detox.