They join to get useful information.
This broadly applies to all communities. Very few people join a community to experience a strong sense of community. They join for immediate gratification.
A sense of community is something that sneaks up on you when you weren’t expecting it.
You might join to ask a question, get advice, not miss out on useful tips. But over time, through these interactions and what you read, you begin to feel a commonality with others. You participate in rituals and traditions. You get to know other members and feel you’re a part of something together.
This can happen purely by chance, but it’s also something you can directly facilitate.
The sense of community isn’t something you promote to visitors and newcomers, it’s something you promote to (and facilitate between) existing members.