It has to do with Vmcg below 14,400kg. Supposedly there is a remote chance that should you have an engine failure below this weight and you have the yaw damper on it may and I repeat may- remote chance of course, on a narrow strip ie less than 30meters cause you to run off the strip. Of course all other limitations such as X/wind of 36 knots max still are ok.
A classic case of ass covering by a big manufacturer.