When creating a new SysML Parametric Diagram for an element which cannot be the context of this diagram (e.g. Package), the new context element (which is a Block) is created automatically.
SysML Plugin 19.0 LTR Documentation
When creating a new SysML Parametric Diagram for an element which cannot be the context of this diagram (e.g. Package), the new context element (which is a Block) is created automatically.