I'm not allowed join an open facebook group?

[Mujer Alta]

Whoever moderates the group - usually whoever started it - determines who gets in. With 7,000 members, the group you're trying to get into might be closed. Maybe they are only admitting new members with a recommendation from someone who already belongs. You can never know why your request to join them is turned down but a 7,000 member group, especially if it's active and moderated, is a huge amount of responsibility and work for whoever's in charge.