Back in 2014 I suggested this idea for ArcMap. This has never been implemented and this issue still persists in the modern ArcGIS Pro. I can copy feature layers from one map to another but I cannot right click on a standalone table, copy and then paste that into the TOC of a new map. Currently, as it is still in ArcMap, I have to add the table via the catalog pane. Would be nicer and quicker if I could copy 'n' paste as I can do with layers.