The Lead Link may exclude some role holders from the core circle members, regarding their effective contribution of the role to the purpose of the circle (little role with very minor contribution, around 5% of time needed for enacting the role).
See constitution (de minimis rule):
2.3.3 EXCLUSION FOR MINOR ALLOCATIONS
Sometimes, a Partner allocates only a very minor, nearly insignificant
amount of attention to a Defined Role in a Circle. If the Circle ’s Lead
Link reasonably believes this is the case, the Lead Link may exclude that
Partner from serving as a Core Circle Member as a result of that Role
Hope that helps,