Unused images - complete with all their thumbnails - are hard to get cleaned up. That is fine when your site is new, but for image-heavy sites it becomes a real pain point with hosting storage limits after a while.
First, we need a way to actually locate truly unattached images. As an example, if you use the Media Library's "unattached" locator you will be given a list of all the images on your WooCommerce Product pages. In other words, that's useless.
Then we need a safe-as-possible way to delete all the thumbnails with the image. It seems like all this should be in core but I've been waiting for it for years and now with the block editor in the works we can count on not seeing it.