In terms of refinement difficulty, the "Da Luo Pill" and the "Luo Tian Pill" are actually not that different.
However, because the Luo Tian Pill is a high-grade immortal pill, it can only be crafted by a high-grade immortal alchemist. Furthermore, high-grade immortal alchemists are far rarer than their mid-grade counterparts. When you add in the fact that the recipe for the Luo Tian Pill is nowhere near as widely circulated as that of the Da Luo Pill, the value of the Luo Tian Pill becomes incomparable to that of the Da Luo Pill.
Even a prince’s estate in a mid-grade immortal kingdom could produce a few Da Luo Pills. For instance, the Prince Qin estate in the Cloud Cliff Immortal Kingdom, where Duan Lingtian previously resided, offered six Da Luo Pills as a prize for the county backing the top three finishers in the "Sixteen-County Martial Gathering."
Chapter 2730