Except that they aren't because they are literally collected at the end of the show and they can easily be opened and the batteries replaced. So they can be used from show to show.
Edit: From their sustainability page it seems like they're actually "refurbished" and reused. :+1:
The thing is: if it's more profitable to make new ones than to reuse the old ones, they most certainly will go that way.
These guys clearly planned ahead :-)
Maybe in some cities they were collected? Not in mine.