Communities that struggle for activity often have no programme of planned activities.
You can succeed without regularly organizing activities, but it's harder. Activities, typically events, play an important role in communities besides directly stimulating activity.
For example, a community of practice might have a debate around a major question within the topic. An interest community might have a live chat about their best memories/funniest stories involving the topic
Major events help too. They help build a sense of connection between members. They help communities develop a shared history. They increase the level of contact between members, facilitate stronger relationships, and increase commitment to the community.
There are rules behind good events. You want people to interact with each other around a common theme. You want active participation, not passive learning.
If you want more participation, putting together a clear plan of events is a great place to start.