Storage rings are not commonly seen.
Before Zhao Changhe obtained one from the Xuanwu Secret Realm, the only other was with Sisi, who inherited it from the ancient Spirit Clan, known for possessing quite a few ancient artifacts. Even though Yuxu's Ying Wu and his group have not been seen using one, they likely have them, and those like Vermilion Bird and Xuanwu who received Ancient Four Symbols inheritance probably possess them as well. Overall, they're extremely rare and only those closely tied to ancient times have them.
Even Tang Wanju didn't have one before, until she recently got one from the palace collection, granted by Your Majesty Chichi. The source is unknown; perhaps Xia Longyuan obtained it in his early years, or it might be tributes accumulated over the years. These kinds of treasures are not abundant in the palace either, considered rare finds.
Thus, Tang Wanju never considered these rare treasures could be applied on a large scale, nor did Tie Muer, likely.
