There were two reasons for this.
First, Sword Qi is sharp and fierce. During cultivation, it often assails a Cultivator's Physical Body. Without a powerful physique, it is difficult to achieve much in the Sword Dao.
Second, Body Refining Cultivators find it easier to pass the "Physical Body Barrier."
For example, when Song Changsheng broke through to Foundation Establishment, the "Spiritual Power Barrier" tormented him half to death, but he passed the "Physical Body Barrier" with ease.
In Major Sects with deep foundations, like the Golden Crow Sect and the Celestial Vein Sect, the core disciples almost all practice the Dual Cultivation of Body and Dharma.
As for the legendary Five Great Holy Lands, the Dual Cultivation of Body and Dharma is standard for all disciples...
