[The arrival of the Stupa of Treasures] is a marvelous story, full of special imagery, cosmological in scope. But clearly such imagery is not so much for the purpose of explaining the nature of the cosmos as it is for extolling, first the Lotus Sutra, second Śākyamuni Buddha, and thirdly this sahā world.

Extolling the Lotus Sutra is both explicit in the chapter and implicit in the story. Many Treasures and the buddhas of the ten directions all come to the sahā world at least in part to hear the Lotus Sutra preached. In this way the Stupa is subordinated to the preaching of the Dharma. I take this to mean that the construction and worship of stupas and the remains of the Buddha are not rejected but are relativized, made subordinate to the Dharma and in particular to the Dharma expressed in the Lotus Sutra.
A Buddhist Kaleidoscope; Gene Reeves, The Lotus Sutra as Radically World-affirming, Page 181