Thank you for your feature request. I understand your desire to provide a sense of scale to your users while they use the map. It is an important aspect of UX.
There is, however, a rationale for why we exclude scale bars. With the invention of zoomable, pannable "slippy" maps, scale bars have become misused and misunderstood tools. This is particularly true on Web Mercator projected maps.
If the map is medium or small scale (shows any area larger than a city), the scale bar is wildly inaccurate and will in fact give your map users absolutely incorrect references. Scale bars are only accurate along two parallel lines of the projection. So using a scale bar will be wildly misleading and inaccurate in those circumstances. (This is why Greenland looks as big as Africa, when in Africa is 18-times the size of Greenland.)
However, there is a bit of a work around for analysts. You can use the Measure Tool in the Analysis Pane. It will tell you an accurate distance. Unfortunately, it's not really useful for a casual user.
I just wanted to shed light on why scale bars haven't been added yet.
I understand your rationale and agree with you – it would be nice to have users have a sense of scale. Alas, with zoomable maps and Web Mercator projections, a scale bar outside of city-wide areas, isn't a good solution either, unfortunately.
Thanks for using ArcGIS for MS365 and for engaging with us on Community!
