They aren't - but are typically made of ash or maple. This is a matter of wood strength and weight with the least chance of warping.
Teak is a hardwood. Pine is a softwood.
Pine is softwood.
pine
Pine is a soft wood. Generally speaking, Trees with leaves are hardwood, Trees with needles are softwood.
All spruce, pine and fir is softwood.
Softwood
Pine is considered a softwood. As a general rule conifers are softwood and deciduas trees are hardwood. This is not always the case but there are not many exceptions.
Ash Balsa Ebony
pine
Pine, like all other conifers, is classified as a softwood.
A pine is a softwood no matter how hard the heartwood is.
brown