It will be available in next release, like it or not 😉
It's not only about storage. Many users are on paid hosting, and not only do they have storage limits, but sometimes "node" limits also (amount of files). Sometimes, users might even have problems opening the cache folders, because there are too many files inside. Right now, if you rename a folder with 1000 images, it will create 1000 new image cache files, and the old ones will never get removed. The same goes for folder cache and menu cache ... As new cache items get created whenever something changes, all the old files will remain. This is very inefficient.
After a while, a large gallery might have 100.000+ cache files, where only 10% of the files are valid.
So let's clean up the cache once in a while, it's automated anyway. If you don't like it, you can disable it ...