This isn't a new stance like.. at all, there are articles from 2014 where yoshi-p pretty much had the same stance with the same in between the lines:
You can use harmless plugins but don't show/advertise it and force us to police you.
Now especially with some bigger WoW streamers coming over using plugins on stream it apparently just got a bit too comfortable and highlighted, so they had to take action (even if it was more of an exemple.)
Also the Issue many people don't realize yet... combat plugins are completely unshackled in this game, you can do so much broken shit with them if you wanted to trivializing fights more than WoW addons would be ever able to because there is no api tools given or moderation in place, you can literally do everything and go crazy, so they are kind of obligated to shut stuff down if it starts to get a bit too comfortable.