Why Lankavatara Sutra was replaced with Diamond Sutra by 5th patriarch?

As far as I know, Lankavatara Sutra was held in high esteem by both Bodhidharma & his disciple Huiko to the extent both based their way of enlightenment on this Sutra. But what it is seen that 5th patriarch Hunjeng recommended his disciple Diamond Sutra. From there onwards, Diamond Sutra took the central position in Zen. What was the reason for this gradual replacement of Lankavatara with Diamond Sutra?