I don't think it comes down to haynes wanting to do one, I think it comes down to what information the manufacturers are prepared to let them have, and for which market the manual is aimed at.

The mk1 manual would have been fairly straight forward to market in Britain, but it isn't offically available, also once you compare it to the BGB you realise how info they just copy over and print off as there own.

Even some of the diagrams are the same.

hth.
