Quite a lot can control why a tab is visible to an attendee or why it is not: 

1.  Roles.  This is a permanent set of controls for your event. You typically won't be switching these mid event.  Role restrictions determine what an attendee of that Role can do and what they cannot do.   Can they book a hotel or do activities?  Can they make requests, who to, and can they create a meeting for themselves?  Can they change blackouts or availability? These settings are configured on the back-end by MeetMax Technical Services during the initial event setup.

2.  Permissions.  This is under Configure -> Event Settings. You may decide that for the first few weeks of your event, you do not want any Activities to be booked. You can uncheck the Permissions for Activities to remove it from the Attendees till you choose to switch it on again.  This setting affects all participants.

3.  Menu Control.   Under Configure -> Site Design -> Menu Editor.  Here you can choose more specifically which tabs are available and for who.  So you may want Activities to be available for a certain Role, or for people who have Paid, or people who have been Approved. Visit our knowledge base article Using the Menu Editor for more.

4.  No Data.  The Activities tab will not be visible if you have not set up any activities.  The Blackouts or Availability tab will no be available if you have not added time slots.  The Hotels tab will not appear till you add a hotel block.  The transportation tab needs transportation options.