Because you are using an old version of the betzaNew.js script, which does not support that parameter yet. (Or you are using betza.js.)
BTW, I made another refinement to provide more control over the layout of the automatically generated buttons: when a set name starts with an asterisk, it removes that asterisk from the name, and puts the button on a new line. (I tested this in your Diagram.)
Because you are using an old version of the betzaNew.js script, which does not support that parameter yet. (Or you are using betza.js.)
BTW, I made another refinement to provide more control over the layout of the automatically generated buttons: when a set name starts with an asterisk, it removes that asterisk from the name, and puts the button on a new line. (I tested this in your Diagram.)