Those are uncompressed folders which each contain the default maps (Booty Bay, Avalanche, etc)
They are supposed to be hidden and all show the maps in one folder, but Reforged broke the archives and now we can see the raw storage folders
When you delete them, Blizzard re-downloads them as they're considered essential, being part of the original installation
Hello, hope this doesn't count as an unnecessary necro. This thread pops up when I search "WC3 downloads stop directorys/folders creation" or some combination of words thereof on Google, so I imagine other people are also being funneled here. Since there's no solution presented here, decided to post my own (works for Windows 10):
What you can do is prevent WC3 from making folders in your C:\Users\[USERNAME]\Documents\Warcraft III\Maps\Download by modifying the permissions. Right click Downloads, then switch to the Security tab, select Advanced. Select Disable inheritance - when prompted select Convert inherited permissions into explicit permissions on this object. Select your username and select Edit. Select Show advanced permissions then uncheck Create folders / append data. Finally, select OK -> OK -> OK.
As long as you're not running WC3 as administrator, this should prevent it from creating folders, and therefore the maps, in your downloads.