Cultivators also needed to be calculative. When the pain you suffered was not proportional to the gains you received, naturally no cultivator would be willing to learn such a cultivation technique.
The five elements body forging technique was such a technique. After cultivating it, it would not be much stronger than other body forging techniques. It might not even be as good as some high-level body forging techniques. However, the pain it would have to endure would be several times or even more than ten times that of other techniques. It was because of this reason that very few people would cultivate the five elements body forging technique.
The main reason why Qin Feng emphasized that Leng Yue cultivated the five elements body tempering art was because this cultivation art could be converted into the unyielding sect's evil Buddha Lotus flower body. Furthermore, it was the cultivation art with the best conversion rate.