The header of each page shows how many followers that page has. That's good because it's important information.
But for groups (members) and events (attendees) this information is missing.
Why is this difficult?
When creating private groups, events and pages, it is important for guests to know how many members a group/event has. With a private group/event this information is then only readable from the header.
But in order to decide to join a group, it makes sense to know how many members it has beforehand.
In the photos I have marked with green line how it is good with pages. With the red line I mark the missing information with groups and events. Please keep in mind that for private pages and events the guest only sees the profile header.