Why can't I insert a vector image directly from the add-in?

Currently, vector images for Office add-ins are not broadly supported by Microsoft's Insert API for add-ins. Microsoft is improving this support and we will add that functionality when it is widely available. For now, all vector images are converted to PNGs before being inserted.

 

If you need to insert the vector file, you can select the "More sizes" option (next to the insert button) and choose Original size. That will download a local copy of the original (vector) file and you can insert it manually into your slide.