Paper manuscripts in South Asia

Birgit Kellner asks on the Indology list which are the oldest dated paper manuscripts in India and Nepal, mentioning for India a mns dated 1198 and for Nepal a mns dated 1105. Why did paper manuscripts remain comparatively rare until recent times, then? Was paper too expensive? Were trade-routes from China and Tibet not commonly used? After all, paper was well spread in China and Tibet since much older time.