Li Xu didn't want to continue the engraving and infusion process, not because he didn't wish to, but because further engraving and infusion would not be cost-effective.
Looking at the cost of engraving and strengthening in the Third Stage, one would realize that to not lose out, the cost would become astronomical. Under normal circumstances, no Contractor could achieve this within one or two years; it would likely take a strong effort of accumulating over four or five years.
Perhaps leaders of great forces like Li Xu could progress faster, but what would be the point if only a rare few became stunning and extraordinary? What he was after wasn't strength enhancement or exchange, nor to become the Main God or to build the Main God Space, but profit, profit, profit!
Important matters need to be said three times!