I run a team and create many meeting requests.

When I create a new Appointment, I go to scheduling and choose attendees ...
Their availability shows as bars of busy time and 'clear' gaps.

On some of the 'busy time' bars I can hover cursor over the bar and it tells me what the appointment is for.
However on most of them there is no information .. what do I need to set, or what do I need to get them to set to allow me to view what appointments/meetings they have for those bars.