Each one has an active sub (one way or another) so 10 Druids played by one person or 10 individual players makes no difference to Blizzard. In fact those multi herbers are buying gametime with gold, which is worth more than a paid sub in the end.
I multibox 3 myself for fun and have always hated the 10 box farmer type… they are not true multiboxers - they are opportunists. This is due to the token.
They banned all broadcasting of keystrokes, it’s no longer possible to press 1 button to send a spell to multiple windows.
https://eu.forums.blizzard.com/en/wow/t/policy-update-for-input-broadcasting-may-2021/275501/3
However this won’t stop them at all… I multibox without any software. It is still allowed.
I think that Blizzard thought they would cripple botting this way but I doubt it has.