Hey Toby!
It was a matter of form accomodating function.
You see, for many years, my fantasy, my dream bass was a 7-String with a 3-octave (36 fret) neck.
Then one day, lo and behold I saw a picture of such a beast -a Conklin Sidewinder with 7 strings and 36 frets.
When I looked at the picture of this bass, I found that it had only one pickup; and there wasn't really much of a place for a second pickup... at best, a second pickup might be able to be positioned right next to the... well, it was more a less a bridge pickup... positionwise. And then, what would be the point?
So, when I decided to commission Alembic to make my dream bass, I modified this original concept slightly -by adding an extra string, and cutting back the fingerboard 5 frets.
So my bass has the same range as a 7-string with 36 frets. Now, I wanted to leave my bridge pickup as close to the normal spot as possible... but the treble end of the pickup is displaced by the extended fingerboard.
So that's it. The slant is just the result of pushing the treble end of the pickup out of the way of the extended fingerboard.