The rational for choosing Draw-IO as a diagramming tool is it's outstanding availability & it's ensured continued availability. Draw-IO is an online available tool accessible on www.draw.io but more importantly an open source tool which therefor can not only be self hosted but also has integrations available which greatly simply said self hosting. Draw-IO has a number of docker containers available for almost any platform there is even an chrome OS app. The XML output by draw-io is standardized and can be easily exported and imported. Therefor Draw-IO is deemed an excellent choice as diagramming tool.