AndroidCentral explains why apps stored on the SD card stop working after updating to KitKat.

It’s simple, really. Prior to Android 4.4 KitKat, applications — provided they had permission to access the SD card — could read and write to any area on removable storage, including the system folders like DCIM, Alarms, etc. That has all changed, and now third-party applications — as in ones you download from Google Play or elsewhere — can only write to files and folders that they have created or have taken ownership of.

This should have been how it was designed from the start. There are people who say they will not update to KitKat because of the hassle to work around the change in SD card support. But if you wanted things to work out of the box, perhaps you should have considered iOS. Isn’t the draw of Android, or so I’ve been told, its flexibility in allowing users to handle the files and folders?

Of course, you can choose not to upgrade. You just need to be very careful with the apps you install and trust that the apps you choose to install have no malicious intents.