Lex nodded as he watched the sanctuary being built. Knowing that it would take years to complete made him feel assured about only using 10 materials for now. While Dao materials were difficult to use up, they were also especially valuable. Between the Butter Knife, his own cultivation and the system requiring Dao materials as payment for anything he wanted to do, he had to be especially calculative about how he acquired these resources.
Dao materials were not things he could get his hands on himself, so it was entirely possible that these would be the last Dao materials he got for a very long time - maybe even until he became a Dao Lord himself. These things were uncertain.
So, until he actually had a personal need for the Dao of Sanctuary, he was not interested in submitting the 40 other Dao materials required to build this thing.
