I too have often found many dozens of Gb's eaten up by these cache files, and I rarely run ArcMap anymore, so I became slightly suspicious...
After a bit of digging, I discovered that the BmLCacheV2 cache files are created when you add basemap layers to a map; AND this happens if you are using either ArcMap or ArcPro. The source of the BGL's is less obvious, but at least some of the Living Atlas datasets create BGL caches (e.g. Current Wind and Weather Conditions). Try deleting the contents of either the BGLCacheV2 or the BmLCacheV2 folders, and then adding various basemap layers, or Living Atlas datasets.
The question is why doesn't ArcMap or ArcPro clear the cache contents once the application closes? The files create instantly in most cases, so you should really only need a cache of the currently open MXD or APRX's. By not clearing them, and allowing these cache files to (in some cases completely) consume unsuspecting users drives, is unnecessary.
arcmap10.4 arcgispro 2.1 cache base maps #livingatlas