Many conditions were required to repair a weapon. First of all, divine weapons (including medicinal cauldrons) were all spiritual objects. When they were forged, they needed a large amount of true Qi, and so did the repair!
Otherwise, the requirements for the environment would also be very harsh! It had to be repaired in a place with abundant spiritual Qi, or else the repair would likely fail! It was the same for alchemy. However, there was a medicinal cauldron for alchemy. True Qi could be poured into the medicinal cauldron to gather together. However, weapons could not be placed in something like a medicinal cauldron. This was because weapons came in all shapes and sizes. It was impossible to forge a unified container for them.
Of course, it might be difficult for others to find a place with such an abundance of Qi, but it wasn't a problem for Lin Yi, who had a godly tool like the Jade. All he had to do was bring the cauldron to the Jade space and fix it.
