According to the Google Dashboard for Android's stats, KitKat is currently taking a 17.9% share in the overall distribution and it’s really unsatisfactory knowing that such a needed feature can be taken away from it.
But you should know that Google actually removed write access for security reasons to stop apps from dumping files all over your sd card which is later a pain to clean up because in most cases even after the app in question has been uninstalled, the files and folders still remain. On the other side, this could become really frustrating especially if your device doesn't have much internal storage available. In the previous versions of Android such as Jelly Bean, the user was able to move certain apps' data to the sd card in order to free up internal memory. Luckaly we're talking about Android here and with root, everything is possible. If you have obtained root access on your device, you will be able to remove this restriction thanks to a few apps.
One app that can do this is SDFix. All you have to do is install the app and follow the on-screen instructions to remove the restriction. An alternative app would be SD KitKat Fixer by the popular developer JRummy. Just like SDFix, the app provides a very simple UI with just one button that says 'FIX'.
With the help of these apps, you will gain the ability to write to your SD card once again just like in the good old Jelly Bean days.