This is because it is said that furnitures do absorb the Qi from its surroundings and for example when we purchase a home, a FS Master would normally also ask who were the previous owners especially if the house has been built for quite some time. This is the same rationale used to check on the antique furniture's origin. For the dining table, one of the best materials is still wood. New furniture needs sometime to absord Qi from it's surrounding. This is mainly because of land scarcity and the need to cremate the dead.
Cremation is said to have a neutral effect on the decendants of the dead.
In the present day, there are many furniture designers and furniture makers. It is not possible to use the measurements on the Feng Shui ruler. Even if som e furniture makers are aware of it, they may not believe in Feng Shui. Most of us are not able to custom design home furnitures. This is a sensible approach and the most practical in today's world.