You can format your code: Code Formatting
I just tried this:
myDiagram.add(
$(go.Part,
{ resizable: true, resizeObjectName: "PIC" },
$(go.Picture, { name: "PIC", desiredSize: new go.Size(580, 580), source: "images/tiger.svg" })
));
and it displayed and interactively resized correctly.
However, I am using Firefox, and I remember now that you are using Internet Explorer. Sure enough, it appears that Internet Explorer does not seem to support resizing of SVG images. I don’t know that there is anything that we can do about that.
One work-around that does work in all three major browsers, with different resizing behavior, is using a “Viewbox” Panel:
myDiagram.add(
$(go.Part, "Viewbox",
{ resizable: true },
$(go.Picture, { desiredSize: new go.Size(580, 580), source: "images/tiger.svg" })
));