Why is the MD SysML <<ConstraintParameter>> implemented as a Port, rather than just a Property ?

A constraint parameter is a property of a constraint block.

When a constraint parameter is displayed in a parametric diagram on a usage of its constraint block it is displayed using a "small box notation" very similar to the existing port notation. Since a Port is a Property anyway it makes sense to leverage the existing port drawing facility. Everywhere a port is used as a constraintg parameter it is clearly named 'parameter'.